late 14c., "that can be felt, perceptible by the touch," from Late Latin palpabilis "that may be touched or felt," from Latin palpare "touch gently, stroke," a word de Vaan finds to be of no known etymology (rejecting the connection in Watkins, etc., to a reduplication of the PIE root *pal-, as in feel (v.), on phonetic grounds). Some sources suggest it is onomatopoeic. The figurative sense of "easily perceived, evident, clear, obvious" also is from late 14c., on the notion of "seeming as if it might be touched." Related: Palpably; palpability.
1620s, "action, state, or condition of touching," from Latin contactus "a touching" (especially "a touching of something unclean, contamination"), from past participle of contingere "to touch, seize," from assimilated form of com "with, together" (see con-) + tangere "to touch," from PIE root *tag- "to touch, handle."
The figurative sense of "a connection, communication" is attested from 1818. The meaning "a person who can be called upon for assistance" is attested by 1931. As a call to the person about to spin an aircraft propeller to signal that the ignition is switched on, contact was in use by 1913.
To make contact (1860) originally was in reference to electrical circuits. Contact lens " thin artificial lens placed directly on the surface of the eye to correct visual defects" is first recorded 1888, in a translation of an article published in Zurich in 1887 by A. Eugen Fick; contacts for "contact lenses" is from 1957. Contact sport, for one involving bodily contact, is attested from 1922.
"walking on the whole sole of the foot" (opposed to digitigrade), 1831, from French plantigrade "walking on the sole of the foot" (1795), from Latin planta "sole of the foot" (from nasalized form of PIE root *plat- "to spread") + gradi "to walk, go, step" (from PIE root *ghredh- "to walk, go"). Used of man and quadrupeds (bears, etc.) whose heels touch the ground in walking.
"publisher's inscription at the end of a book," 1774, from Late Latin colophon, from Greek kolophōn "summit, final touch" (from PIE root *kel- (2) "to be prominent; hill"). "In early times the colophon gave the information now given on the title page" [OED].