postdoc vs research worker

postdoc and research worker both are nouns.

Word	Noun	Adjective	Verb	Adverb
postdoc	Yes	No	No	No
research worker	Yes	No	No	No

As nouns, research worker is a hypernym of postdoc; that is, research worker is a word with a broader meaning than postdoc:

postdoc: a scholar or researcher who is involved in academic study beyond the level of a doctoral degree
research worker: a scientist who devotes himself to doing research

Other hypernyms of postdoc include investigator, researcher, bookman, scholar, scholarly person.

postdoc (noun)	research worker (noun)
a scholar or researcher who is involved in academic study beyond the level of a doctoral degree	a scientist who devotes himself to doing research
a grant that funds postdoctoral study or research