klaxon |ˈklæksn| — a kind of loud horn formerly used on motor vehicles

Kleenex |ˈkliːneks| — a piece of soft absorbent paper (usually two or more thin layers) used as a disposable handkerchief

kleptomania |ˌkleptəˈmeɪniə| — an irresistible impulse to steal in the absence of any economic motive

kleptomaniac |ˌkleptəˈmeɪnɪæk| — someone with an irrational urge to steal in the absence of an economic motive

kluxer |ˈkləksər| — a member of the Ku Klux Klan

klystron |ˈklɪstrɒn| — an electron tube used to generate or amplify electromagnetic radiation in the microwave region by velocity modulation