tense vs future tense

tense and future tense both are nouns.

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

As nouns, future tense is a hyponym of tense; that is, future tense is a word with a more specific, narrower meaning than tense:

tense (noun)	future tense (noun)
a grammatical category of verbs used to express distinctions of time	a verb tense that expresses actions or states in the future

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