researcher vs postdoc

researcher and postdoc both are nouns.

Word	Noun	Adjective	Verb	Adverb
researcher	Yes	No	No	No
postdoc	Yes	No	No	No

As nouns, postdoc is a hyponym of researcher; that is, postdoc is a word with a more specific, narrower meaning than researcher:

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

Other hyponyms of researcher include experimenter, boffin, fieldworker, post doc.

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