1A collar worn by a person. In quot. 1821 figurative: a hangman's noose. Now chiefly historical.
2A collar used in leading, tethering, or harnessing an animal; especially that part of the harness of a draught horse that fits round the base of the neck.
3A collar placed round the neck of an animal as part of a research programme, usually to aid identification.
4A natural band or ring of contrasting colour on the neck of an animal, especially a bird.
5An advertising or branding label placed round the neck of a bottle.
Late 15th century; earliest use found in MS Court Rolls Long Bennington, Lincolnshire. From neck + collar.