The word 'lip' is native English with deep Germanic and possibly Indo-European roots. It descends from Old English 'lippa,' from Proto-Germanic *lepjō (lip), with cognates in German 'Lippe,' Dutch 'lip,' and Swedish dialectal 'läpp.' The deeper etymology connects it to PIE *leb- (to hang loosely, to droop, to be slack), making the lip 'the hanging thing' — the loose fleshy flap at the edge of the mouth.
The relationship between Germanic *lepjō and Latin 'labium' (lip) — the source of English 'labial,' 'labium,' and the French-derived 'label' (originally a strip or flap) — has been debated for over a century. The two words look similar and mean the same thing, but the precise phonological correspondence is difficult to establish with certainty. Some linguists reconstruct a common PIE ancestor, while others treat them as similar-looking words from separate but phonetically close roots. The issue remains unresolved.
Old English had two words for the lip area: 'lippa' (the lip proper) and 'weler' or 'weleras' (the lips, sometimes the mouth as a whole). 'Lippa' won out, and 'weler' disappeared from English entirely.
The metaphorical extensions of 'lip' are varied. The 'lip' of a cup, a jug, or a crater refers to the rim or edge — the part that resembles the edge of a mouth. This sense is attested from the sixteenth century. 'Lip' meaning 'impudent talk' or 'backtalk' ('don't give me any lip') dates from the nineteenth century in American and British slang.
The expression 'stiff upper lip' — meaning stoic composure in the face of adversity — is particularly associated with British national character, though the phrase itself first appeared in American English in the 1830s. The physical image is of keeping the upper lip from trembling (a sign of being about to cry). The phrase was adopted by the British and became strongly associated with Victorian and Edwardian ideals of emotional restraint.
'Lipstick' is a compound dating from the 1880s, though the practice of coloring the lips is ancient — Sumerian women used crushed gemstones on their lips around 3500 BCE, and Cleopatra is said to have used carmine dye from crushed beetles. 'Lip-reading' (interpreting speech by watching the speaker's lip movements) dates from the nineteenth century as a technique taught to deaf individuals.
In phonetics, the adjective 'labial' (from Latin 'labium') describes sounds produced with the lips: bilabial sounds like /b/, /p/, and /m/ (both lips together) and labiodental sounds like /f/ and /v/ (lower lip against upper teeth). The fact that the technical term uses the Latin root rather than the Germanic one is typical of scientific terminology, which has historically preferred Latin and Greek vocabulary.