The term 'Happy as a Lark' is an idiom used to describe someone who is in a very good mood. The crossword solutions for this term are GAY (3 letters), CHIRPY (6 letters), ELATED (6 letters), SUNNY (5 letters), CHEERFUL (8 letters), ONAIR (5 letters), and ONTOPOFTHEWORLD (15 letters). All of these words can be used to describe someone who is in a very good mood, with GAY and CHEERFUL being the most common. ELATED and ONAIR are more intense words, while CHIRPY and SUNNY are more lighthearted. ONTOPOFTHEWORLD is the most extreme word, suggesting that the person is in an ecstatic state.