choice of words vs diction

choice of words and diction both are nouns.

Word	Noun	Adjective	Verb	Adverb
choice of words	Yes	No	No	No
diction	Yes	No	No	No

As nouns, choice of words and diction are synonyms defined as:

choice of words and diction: the manner in which something is expressed in words

Other synonyms of choice of words include phraseology, phrasing, verbiage, wording.

choice of words (noun)	diction (noun)
the manner in which something is expressed in words	the manner in which something is expressed in words
	the articulation of speech regarded from the point of view of its intelligibility to the audience