Same word as lackadaisical:

abstracted, apathetic, daydreaming, disinterested, dreamy, dull, energyless, enervated, faineant, halfhearted, idle, inattentive, incurious, indolent, inert, laid-back, languid, languishing, languorous, lazy, lethargic, limp, listless, moony, passive, romantic, sentimental