careless

1. Taking insufficient care; negligent: a careless housekeeper; careless proofreading.

2. Marked by or resulting from lack of forethought or thoroughness: a careless mistake.

3. Showing a lack of consideration: a careless remark.

4. Unconcerned or indifferent; heedless: careless of the consequences.

5. Unstudied or effortless: danced with careless grace.

6. Exhibiting a disposition that is free from cares; cheerful: a careless grin; a careless wave of the hand.

Synonyms: These adjectives apply to what is marked by insufficient care or attention. Careless often implies negligence: "It is natural for careless writers to run into faults they never think of" (George Berkeley).
Heedless often suggests recklessness: "We have always known that heedless self-interest was bad morals; we know now that it is bad economics" (Franklin D. Roosevelt).
Thoughtless applies to actions taken without due consideration: "But thoughtless follies laid him low / And stain'd his name" (Robert Burns).
Inadvertent implies unintentional lack of care: With an inadvertent gesture, she swept the vase off the table.