rowlock vs holder

rowlock and holder both are nouns.

Word	Noun	Adjective	Verb	Adverb
rowlock	Yes	No	No	No
holder	Yes	No	No	No

As nouns, holder is a hypernym of rowlock; that is, holder is a word with a broader meaning than rowlock:

rowlock: a holder attached to the gunwale of a boat that holds the oar in place and acts as a fulcrum for rowing
holder: a holding device

rowlock (noun)	holder (noun)
a holder attached to the gunwale of a boat that holds the oar in place and acts as a fulcrum for rowing	a holding device
	the person who is in possession of a check or note or bond or document of title that is endorsed to him or to whoever holds it
	a person who holds something