The adjective cynical means believing that people act selfishly. To be cynical about something means you do not believe it can be successful or the people involved are honest.

Synonyms are skeptical, doubtful, distrustful or disbelieving.

The word origins 1518, “resembling Cynic philosophers” with a capital ‘C’. In 1660s the meaning developed (and with a lower case ‘c’) to “disposed to disbelieve or doubt the sincerity or value of social usages or personal character or motives and to express it by sarcasm and sneers, disparaging of the motives of others, captious, peevish.”

He was cynical about politicians’ promises on taxes.

The soft-drink industry cynically continues to target children.

You don’t have a cynical bone in your body.