cheerfulness, cheer, sunniness, sunshine -- (the quality of being cheerful and dispelling gloom; "flowers added a note of cheerfulness to the drab room")
cheer -- (show approval or good wishes by shouting; "everybody cheered the birthday boy")
cheer, cheer up, jolly along, jolly up -- (cause (somebody) to feel happier or more cheerful; "She tried to cheer up the disappointed child when he failed to win the spelling bee")