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careless 
1 absent-minded, cursory, forgetful, hasty, heedless, incautious, inconsiderate, indiscreet, negligent, perfunctory, regardless, remiss, thoughtless, unconcerned, unguarded, unmindful, unthinking 
2 cavalier, inaccurate, irresponsible, lackadaisical, neglectful, offhand, slapdash, slipshod, sloppy  (informal) 
3 artless, casual, nonchalant, unstudied 
 
Antonyms  
 accurate, alert, anxious, attentive, careful, cautious, concerned, correct, neat, on the ball  (informal) orderly, painstaking, tidy, wary, watchful