digger vs dredge

digger and dredge both are nouns.

Word	Noun	Adjective	Verb	Adverb
digger	Yes	No	No	No
dredge	Yes	No	Yes	No

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

Other hyponyms of digger include backhoe, steam shovel.

digger (noun)	dredge (noun)
a machine for excavating	a power shovel to remove material from a channel or riverbed
a laborer who digs

digger (verb)	dredge (verb)
	remove with a power shovel, usually from a bottom of a body of water
	search (as the bottom of a body of water) for something valuable or lost
	cover before cooking