-up

Consult Webster’s. If not listed in Webster’s, hyphenate.

Frequently used nouns and adjectives: breakup. change-up. checkup. cleanup. close-up. cover-up. crackup. followup. grown-up. holdup. letup. lineup. makeup. mix-up. mock-up. pileup. push-up. roundup. runners-up. setup. shakeup. smashup. speedup. tie-up. walk-up. windup.

Use two words when any of these occurs as a verb. Stacy checked up on her dog at lunch. Casswell rounded up from 2.67 to 3.