lackadaisical (adj.) Look up lackadaisical at Dictionary.com
1768 (Sterne), from interjection lackadaisy "alas, alack" (1748), an alteration of lack-a-day (1690s), from alack the day (1590s). Hence, "given to crying 'lack-a-day,' vapidly sentimental." Sense probably altered by influence of lax. Related: Lackadaisically.