post doc vs investigator

post doc and investigator both are nouns.

Word	Noun	Adjective	Verb	Adverb
post doc	Yes	No	No	No
investigator	Yes	No	No	No

As nouns, investigator is a hypernym of post doc; that is, investigator is a word with a broader meaning than post doc:

post doc: 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 post doc include research worker, researcher, bookman, scholar, scholarly person.

post doc (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