'tense up' definitions:

Become tense, nervous, or uneasy; "He tensed up when he saw his opponent enter the room" [syn: tense, tense up] [ant: decompress, loosen up, relax, slow down, unbend, unwind]

Cause to be tense and uneasy or nervous or anxious; "he got a phone call from his lawyer that tensed him up" [syn: tense, strain, tense up] [ant: loosen up, make relaxed, relax, unlax, unstrain, unwind]