completion vs culmination

completion and culmination both are nouns.

Word	Noun	Adjective	Verb	Adverb
completion	Yes	No	No	No
culmination	Yes	No	No	No

As nouns, completion and culmination are synonyms defined as:

Other synonyms of completion include closing, mop up, windup.

completion (noun)	culmination (noun)
a concluding action	a concluding action
(American football) a successful forward pass in football	the decisive moment in a novel or play
	(astronomy) a heavenly body's highest celestial point above an observer's horizon
	a final climactic stage