In the opening paragraph of the Shalosh Regalim Amidah's middle section the phrasing is:
... מועדים לשמחה, חגים וזמנים לששון
This M.Y. answer explains the difference in meaning between שמחה and ששון, generally. Why is a מועד associated with שמחה and חגים וזמנים associated with ששון?