Meaning of TENSE UP

WordNet Dictionary
	Definition:		[v]  make tense [v]  become tense or tenser; "He tensed up when he saw his opponent enter the room"
	Synonyms:		strain, tense
	Antonyms:		decompress, loosen up, make relaxed, relax, slow down, unbend, unlax, unstrain, unwind
	See Also:		affect, change state, crick, extend, stretch, tense up, turn