investigator vs boffin

investigator and boffin both are nouns.

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

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

investigator: a scientist who devotes himself to doing research
boffin: (British slang) a scientist or technician engaged in military research

Other hyponyms of investigator include experimenter, fieldworker, post doc, postdoc.

investigator (noun)	boffin (noun)
someone who investigates	(British slang) a scientist or technician engaged in military research
a scientist who devotes himself to doing research
a police officer who investigates crimes