1869, "something which shuts off;" 1889, "cessation of flow," from the verbal phrase, which is attested from 1824, "turn off, prevent the passage of (gas, steam) by closing a valve, etc."
1580s, "cause to make a weak, sharp, sound" (transitive), of imitative origin (compare Dutch and East Frisian klikken "to click;" Old French clique "tick of a clock"). Intransitive sense "make a weak, sharp sound" is from 1610s.
The figurative sense, in reference usually to persons, "hit it off at once, become friendly upon meeting" is from 1915, perhaps based on the sound of a key in a lock. Mental figurative meaning "to fall into context" is by 1939. Related: Clicked; clicking.
1821, "something that ticks," agent noun from tick (v.); slang meaning "heart" first recorded 1930. Ticker tape (1891) is from ticker "telegraphic device for recording stock market quotations, etc." (1883).
"children's game," 1738 (in reference to "Queen Mary's reign"), perhaps a variation of Scottish tig "touch, tap" (1721), probably an alteration of Middle English tek "touch, tap" (see tick (n.2)). Baseball sense is from 1912. It's not an acronym and doesn't stand for anything.
poison obtained from the castor-oil bean, 1888, from ricinus, genus name of the castor-oil plant (1694), from Latin ricinus (Pliny), a word of uncertain origin, perhaps the same word as ricinus "tick" (in sheep, dogs, etc.). Latin ricinum was used in late Old English herbariums.
"cloth covering (usually of strong cotton or linen) for mattresses or pillows," 1640s, from tyke (modern tick) with the same meaning (mid-14c.), probably from Middle Dutch tike, from a West Germanic borrowing of Latin theca "case," from Greek thēkē "a case, box, cover, sheath," from suffixed form of PIE root *dhe- "to set, put."