In an irritable or depressed state of mind. For example, Dad’s in a bad mood, so don’t ask for anything right now. The antonym, in a good mood, refers to a cheerful, well-disposed state of mind, as in When the boss is in a good mood our whole day goes well. The phrase in a mood, meaning “disposed” or “inclined,” dates from about a.d. 1000. Also see in the mood.