Unclean
The umbrella collects the ceremonial sense of "unclean" — the legal categorization that distinguishes which living creatures may be eaten, which may not, and what kinds of contact transmit defilement. Two parallel catalogues set out the law: Leviticus 11 and Deuteronomy 14. Together they sort animals by category (land, water, air, creeping), name the disqualifying anatomy, and explain that the whole sorting serves Israel's holiness before Yahweh.
The Law of Land Animals
The first cut is anatomical. Among land beasts, only those that both part the hoof and chew the cud may be eaten: "Whatever parts the hoof, and is clovenfooted, [and] chews the cud, among the beasts, that may you⁺ eat" (Lev 11:3). The familiar exclusions are then named one by one: "Nevertheless these you⁺ will not eat of those that chew the cud, or of those that part the hoof: the camel, because he chews the cud but doesn't part the hoof, he is unclean to you⁺. And the coney, because he chews the cud but doesn't part the hoof, he is unclean to you⁺. And the hare, because she chews the cud but doesn't part the hoof, she is unclean to you⁺. And the swine, because he parts the hoof, and is clovenfooted, but doesn't chew the cud, he is unclean to you⁺. Of their flesh you⁺ will not eat, and their carcasses you⁺ will not touch; they are unclean to you⁺" (Lev 11:4-8). The disqualification is double-keyed: a creature must satisfy both criteria; failing either makes it unclean.
Deuteronomy's catalogue starts from the positive list — "the ox, the sheep, and the goat, the hart, and the gazelle, and the roebuck, and the wild goat, and the pygarg, and the antelope, and the chamois" (Deut 14:4-5) — before stating the same rule by anatomy: "And every beast that parts the hoof, and has the hoof cloven in two, [and] chews the cud, among the beasts, that may you⁺ eat" (Deut 14:6). The same four exclusions follow: "Nevertheless these you⁺ will not eat of those that chew the cud, or of those that have the hoof cloven: the camel, and the hare, and the coney; because they chew the cud but part not the hoof, they are unclean to you⁺. And the swine, because he parts the hoof but chews not the cud, he is unclean to you⁺: of their flesh you⁺ will not eat, and their carcasses you⁺ will not touch" (Deut 14:7-8).
Water Creatures
Water creatures sort by fins and scales. "These you⁺ may eat of all that are in the waters: whatever has fins and scales in the waters, in the seas, and in the rivers, that you⁺ may eat. And all that don't have fins and scales in the seas, and in the rivers, of all that move in the waters, and of all the living souls that are in the waters, they are detestable to you⁺" (Lev 11:9-10). The Leviticus formulation extends to a general rule: "Whatever doesn't have fins and scales in the waters, that is detestable to you⁺" (Lev 11:12). Deuteronomy compresses the same rule and adds the unclean label: "These you⁺ may eat of all that are in the waters: whatever has fins and scales may you⁺ eat; and whatever does not have fins and scales you⁺ will not eat; it is unclean to you⁺" (Deut 14:9-10).
Birds and Winged Things
The bird list operates by enumeration rather than rule. "And these you⁺ will detest among the birds; they will not be eaten, they are detestable: the eagle, and the gier-eagle, and the osprey, and the kite, and the falcon after its kind, every raven after its kind, and the ostrich, and the nighthawk, and the seamew, and the hawk after its kind, and the little owl, and the cormorant, and the great owl, and the horned owl, and the pelican, and the vulture, and the stork, the heron after its kind, and the hoopoe, and the bat" (Lev 11:13-19). Deuteronomy's bird list is essentially the same, with minor reordering and the addition of "the glede" (Deut 14:12-18).
Winged creeping things are unclean as a class, with one carved-out exception: "All winged creeping things that go on all fours are detestable to you⁺. Yet these you⁺ may eat of all winged creeping things that go on all fours, which have legs above their feet, with which to leap on the earth. Even these of those you⁺ may eat: the locust after its kind, and the bald locust after its kind, and the cricket after its kind, and the grasshopper after its kind. But all winged creeping things, which have four feet, are detestable to you⁺" (Lev 11:20-23). Deuteronomy takes the simpler line: "And all winged creeping things are unclean to you⁺: they will not be eaten" (Deut 14:19).
Creeping Things on the Ground
A separate enumeration handles ground creepers: "And these are unclean to you⁺ among the creeping things that creep on the earth: the weasel, and the mouse, and the great lizard after its kind, and the gecko, and the land-crocodile, and the lizard, and the sand-lizard, and the chameleon" (Lev 11:29-30). The general rule covers anything else of the same class: "Whatever goes on the belly, and whatever goes on all fours, or whatever has many feet, even all creeping things that creep on the earth, you⁺ will not eat them; for they are detestable" (Lev 11:42).
Defilement by Contact
Beyond the food rules, Leviticus 11 lays out a separate layer concerned with how contact with the carcasses transmits uncleanness. "And by these you⁺ will become unclean: whoever touches their carcass will be unclean until the evening; And whoever bears [anything] of their carcass will wash his clothes, and be unclean until the evening" (Lev 11:24-25). The rule is generalized: "Every beast which parts the hoof, if it is either not clovenfooted, or does not chew the cud, is unclean to you⁺: everyone who touches them will be unclean. And whatever goes on its paws, among all beasts that go on all fours, they are unclean to you⁺: whoever touches their carcass will be unclean until the evening" (Lev 11:26-27).
Vessels and contents inherit the defilement when a carcass falls on them: "And whatever any of them falls on when they are dead, it will be unclean; whether it is any vessel of wood, or raiment, or skin, or sack, whatever vessel it is, with which any work is done, it must be put into water, and it will be unclean until the evening; then it will be clean. And every earthen vessel, into which any of them falls, whatever is in it will be unclean, and it you⁺ will break" (Lev 11:32-33). Wet food and drink are particularly susceptible: "All food [in it] which may be eaten, that on which water comes, will be unclean; and all drink that may be drank in every [such] vessel will be unclean" (Lev 11:34). Two exceptions are noted: a fountain or pit holding water remains clean despite contact (Lev 11:36), and dry seed left for sowing is unaffected unless it has been wetted (Lev 11:37-38). Even an animal of an otherwise edible kind defiles by death: "And if any beast, of which you⁺ may eat, dies; he who touches its carcass will be unclean until the evening" (Lev 11:39).
Deuteronomy adds its own rule on naturally-dead animals: "You⁺ will not eat of anything that dies of itself: you may give it to the sojourner who is inside your gates, that he may eat it; or you may sell it to a foreigner: for you are a holy people to Yahweh your God. You will not boil a young goat in its mother's milk" (Deut 14:21).
Holiness as the Rationale
Both chapters frame the food and contact rules as outworkings of Israel's holiness. Leviticus puts the matter in Yahweh's voice: "You⁺ will not make your souls detestable with any creeping thing that creeps, neither will you⁺ become unclean with them, so that you⁺ should be defiled by them. For I am Yahweh your⁺ God: sanctify yourselves therefore, and be⁺ holy; for I am holy: neither will you⁺ defile your souls with any manner of creeping thing that moves on the earth. For I am Yahweh who brought you⁺ up out of the land of Egypt, to be your⁺ God: you⁺ will therefore be holy, for I am holy" (Lev 11:43-45). The closing summary states the law's purpose: "to make a distinction between the unclean and the clean, and between the living thing that may be eaten and the living thing that may not be eaten" (Lev 11:47).
Deuteronomy's framing is the same: the chapter opens "You⁺ are the sons of Yahweh your⁺ God" (Deut 14:1), repeats "you are a holy people to Yahweh your God" twice (Deut 14:2 and 14:21), and grounds the dietary distinctions in that election. The unclean/clean line is thus not free-standing taxonomy but the practical shape of Israel's belonging to Yahweh.