look back vs retrospect

look back is not a noun while retrospect is a noun.

Word	Noun	Adjective	Verb	Adverb
look back	No	No	Yes	No
retrospect	Yes	No	Yes	No

As verbs, look back and retrospect are synonyms defined as:

look back and retrospect: look back upon (a period of time, sequence of events); remember

Other synonyms of look back include review.

look back (noun)	retrospect (noun)
	contemplation of things past

look back (verb)	retrospect (verb)
look back upon (a period of time, sequence of events); remember	look back upon (a period of time, sequence of events); remember
look towards one's back