retrospect vs look back

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

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

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

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

Other synonyms of retrospect include review.

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

retrospect (verb)	look back (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