Lawn tennis serve sense is from 1903. The kill "the knockout" is boxing jargon, 1950. Killer in slang sense of "impressive person or thing" first recorded 1937; as an adj., 1979. Killjoy is first recorded 1776; formerly used with other stems (cf. kill-courtesy "boorish person," kill-cow "bully, big man," etc.). Sense in to kill time is from 1728. Killer whale is from 1725. Killing "large profit" is 1888, Amer.Eng. slang. Kill-devil, colloquial for "rum," especially if new or of bad quality, is from 1630s.
"stream," 1639, Amer.Eng., from Du. kil, from M.Du. kille "riverbed," especially in place names (e.g. Schuylkill). A common Gmc. word, the O.N. form, kill, meant "bay, gulf" and gave its name to Kiel Fjord on the German Baltic coast and thence to Kiel, the port city founded there in 1240.