ascent vs rapid climb

ascent and rapid climb both are nouns.

Word	Noun	Adjective	Verb	Adverb
ascent	Yes	No	No	No
rapid climb	Yes	No	No	No

As nouns, rapid climb is a hyponym of ascent; that is, rapid climb is a word with a more specific, narrower meaning than ascent:

ascent (noun)	rapid climb (noun)
the act of changing location in an upward direction	a rapid rise
a movement upward; rise above the ground
an upward slope or grade (as in a road)