giant cockroach vs cockroach

giant cockroach and cockroach both are nouns.

Word	Noun	Adjective	Verb	Adverb
giant cockroach	Yes	No	No	No
cockroach	Yes	No	No	No

As nouns, cockroach is a hypernym of giant cockroach; that is, cockroach is a word with a broader meaning than giant cockroach:

giant cockroach: large tropical American cockroaches
cockroach: any of numerous chiefly nocturnal insects; some are domestic pests

Other hypernyms of giant cockroach include roach.

giant cockroach (noun)	cockroach (noun)
large tropical American cockroaches	any of numerous chiefly nocturnal insects; some are domestic pests