tense up vs tense

tense up is not a noun while tense is a noun.

Word	Noun	Adjective	Verb	Adverb
tense up	No	No	Yes	No
tense	Yes	Yes	Yes	No

As verbs, tense up and tense are synonyms defined as:

Other synonyms of tense up include strain.

As verbs, tense up and tense are synonyms defined as:

tense up (noun)	tense (noun)
	a grammatical category of verbs used to express distinctions of time

tense up (adjective)	tense (adjective)
	taut or rigid; stretched tight
	pronounced with relatively tense tongue muscles (e.g., the vowel sound in `beat')
	in or of a state of physical or nervous tension

tense up (verb)	tense (verb)
cause to be tense and uneasy or nervous or anxious	cause to be tense and uneasy or nervous or anxious
become tense, nervous, or uneasy	become tense, nervous, or uneasy
	increase the tension on
	become stretched or tense or taut