"of or pertaining to a breast," 1680s, from French mammaire (18c.) or Medieval Latin mammarius, from Latin mamma "breast" (see mamma).
plural papillae, 1690s, "a nipple of a mammary gland," from Latin papilla "nipple," diminutive of papula "swelling" (see pap (n.2)). Meaning "nipple-like protuberance" attested from 1713.
before vowels mast-, word-forming element meaning "female breast, mammary gland," from Greek mastos "woman's breast," from madan "to be wet, to flow," from PIE *mad- "wet, moist, dripping" (source also of Latin madere "be moist;" Albanian mend "suckle;" see mast (n.2)).
"an animal of the class Mammalia; an animal that suckles its young," 1826, Englished form of Modern Latin Mammalia (1773), coined 1758 by Linnaeus for that class of animals from neuter plural of Late Latin mammalis "of the breast," from Latin mamma "breast," which is cognate with mamma. With the exception of a few egg-laying species, all bear live young and have the mammary gland for the young to suck. All also are warm-blooded and breathe air. In Middle English, mammille was "a woman's breast" (early 15c.).
Old English breost "mammary gland of a woman, bosom; the thorax or chest, part of the body between the neck and the belly; mind, thought, disposition," from Proto-Germanic *brust-/*breust- "breast" (source also of Old Saxon briost, Old Frisian briast, Old Norse brjost, Dutch borst, German brust, Gothic brusts), perhaps literally "swelling" and from PIE root *bhreus- "to swell, sprout" (source also of Middle Irish bruasach "having a broad, strong chest," Old Irish bruinne "breast").
The spelling conforms to the Scottish and northern England dialectal pronunciation. Figurative sense of "seat of the emotions and affections, repository of designs and secrets" was in Old English. Breast-plate "armor for the front of the body" is from late 14c. Breast-pump is from 1821.
"opaque white fluid secreted by mammary glands of female mammals, suited to the nourishment of their young," Middle English milk, from Old English meoluc (West Saxon), milc (Anglian), from Proto-Germanic *meluk- "milk" (source also of Old Norse mjolk, Old Frisian melok, Old Saxon miluk, Dutch melk, Old High German miluh, German Milch, Gothic miluks), from *melk- "to milk," from PIE root *melg- "to wipe, to rub off," also "to stroke; to milk," in reference to the hand motion involved in milking an animal. Old Church Slavonic noun meleko (Russian moloko, Czech mleko) is considered to be adopted from Germanic.
Of milk-like plant juices or saps from c. 1200. Milk chocolate (eating chocolate made with milk solids, paler and sweeter) is recorded by 1723; milk shake was used from 1889 for a variety of concoctions, but the modern version (composed of milk, flavoring, etc., mixed by shaking) is from the 1930s. Milk tooth (1727) uses the word in its figurative sense "period of infancy," attested from 17c. To cry over spilt milk (representing anything which, once misused, cannot be recovered) is first attested 1836 in writing of Canadian humorist Thomas C. Haliburton. Milk and honey is from the Old Testament phrase describing the richness of the Promised Land (Numbers xvi.13, Old English meolc and hunie). Milk of human kindness is from "Macbeth" (1605).