Is it ensure, insure, or assure?
early 15c., "one of a series of rings or loops which form a chain; section of a cord," probably from Old Norse *hlenkr or a similar Scandinavian source (cf. Old Norse hlekkr "link," Old Swedish lænker "chain, link," Norwegian lenke, Danish lænke), from Proto-Germanic *khlink- (cf. German lenken "to bend, turn, lead," gelenk "articulation, joint, link," Old English hlencan (plural) "armor"), from PIE root *kleng- "to bend, turn." Missing link between man and apes dates to 1880.
"torch," 1520s, of uncertain origin, possibly from Medieval Latin linchinus, from lichinus "wick," from Greek lykhnos "portable light, lamp."
"bind, fasten, to couple," late 14c., believed to be from link (n.), though it is attested earlier. Related: Linked; linking.