union member vs trade unionist

union member and trade unionist both are nouns.

Word	Noun	Adjective	Verb	Adverb
union member	Yes	No	No	No
trade unionist	Yes	No	No	No

As nouns, union member and trade unionist are synonyms defined as:

Other synonyms of union member include unionist.

union member (noun)	trade unionist (noun)
a worker who belongs to a trade union	a worker who belongs to a trade union