lighter vs dredger

lighter and dredger both are nouns.

Word	Noun	Adjective	Verb	Adverb
lighter	Yes	No	Yes	No
dredger	Yes	No	No	No

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

Other hyponyms of lighter include houseboat, pontoon, scow, Norfolk wherry, wherry.

lighter (noun)	dredger (noun)
a device for lighting or igniting fuel or charges or fires	a barge (or a vessel resembling a barge) that is used for dredging
a flatbottom boat for carrying heavy loads (especially on canals)
a substance used to ignite or kindle a fire

lighter (verb)	dredger (verb)
transport in a flatbottom boat