bullet vs dumdum bullet

bullet and dumdum bullet both are nouns.

Word	Noun	Adjective	Verb	Adverb
bullet	Yes	No	No	No
dumdum bullet	Yes	No	No	No

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

bullet: a projectile that is fired from a gun
dumdum bullet: a soft-nosed small-arms bullet that expands when it hits a target and causes a gaping wound

Other hyponyms of bullet include dumdum, full metal jacket, rifle ball, rubber bullet.

bullet (noun)	dumdum bullet (noun)
(baseball) a pitch thrown with maximum velocity	a soft-nosed small-arms bullet that expands when it hits a target and causes a gaping wound
a projectile that is fired from a gun
a high-speed passenger train