completion vs closing

completion and closing both are nouns.

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

As nouns, completion and closing are synonyms defined as:

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

completion (noun)	closing (noun)
a concluding action	termination of operations
(American football) a successful forward pass in football	the act of closing something
	a concluding action
	approaching a particular destination; a coming closer; a narrowing of a gap
	the last section of a communication

completion (adjective)	closing (adjective)
	final or ending