pill n.

mid-14c., "downy plumage;" late 15c, "fine, soft hair," from Anglo-French pyle or Middle Dutch pijl, both from Latin pilus "a hair" (source of Italian pelo, Old French pel), a word of uncertain origin. Phonological evidence rules out transmission of the English word via Old French cognate peil, poil. Meaning "soft, raised surface of a regular and closely set kind upon cloth" is from 1560s.

"to strip off" the skin, bark, or rind from, developed from Old English pilian "to peel, skin, decorticate, strip the skin or ring," and Old French pillier, both from Latin pilare "to strip of hair," from pilus "hair" (see pile (n.3)). Probably also influenced by Latin pellis "skin, hide." Related: Peeled; peeling. Intransitive sense of "to lose the skin or rind" is from 1630s.

The figurative expression keep (one's) eyes peeled "be observant, be on the alert" is by 1852, American English, perhaps a play on the potato "eye," which is peeled by stripping off the skin. Peel out "speed away from a place in a car, on a motorcycle, etc.," is hot-rodders' slang, attested by 1952, perhaps from the notion of leaving behind a "peel" of rubber from the tire as it skids. Aircraft pilot phrase peel off "veer away from formation" is from World War II; earlier American English had slang peel it "run away at full speed" (1860).