postdoc vs investigator

postdoc and investigator both are nouns.

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

As nouns, investigator is a hypernym of postdoc; that is, investigator 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
investigator: a scientist who devotes himself to doing research

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

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