Blithe
Part of speech: adjective
Definition: Happy, cheerful. Indifferent, careless, showing a lack of concern.
Unconcerned
Part of speech: adjective
Definition: Indifferent and having no interest; aloof.Not worried, anxious or apprehensive.
Example sentence: What's distinctively shocking about Machiavelli is that he didn't care. He believed not only that politicians must do evil in the name of the public good, but also that they shouldn't worry about it. He was unconcerned, in other words, with what modern thinkers call 'the problem of dirty hands.'