trade unionist vs union member

trade unionist and union member both are nouns.

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

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

Other synonyms of trade unionist include unionist.

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