- an eccentric or irrational person; a nut: When the FBI first looked into him, they thought he was a harmless screwball.
- a pitched ball that curves toward the side of the plate from which it was thrown, in a trajectory opposite to that of a curve ball: Has the once popular screwball vanished completely from the major leagues?
- eccentric or irrational; nutty: What a screwball idea!
- an odd or eccentric person
- odd; zany; eccentric
