lack·a·dai·si·cal (lāk'ə-dā'zĭ-kəl) adj. Lacking spirit, liveliness, or interest; languid: "There'll be no time to correct lackadaisical driving techniques after trouble develops"(William J. Hampton).
[From lackadaisy, alteration of lackaday.] lack'a·dai'si·cal·ly adv., lack'a·dai'si·cal·ness n.
1768, from interjection lackadaisy "alas, alack" (1748), an alteration of lack-a-day (1695), from alack the day. Hence, "given to crying 'lack-a-day,' vapidly sentimental." Sense probably altered by infl. of lax.