fish joint vs butt joint

fish joint and butt joint both are nouns.

Word	Noun	Adjective	Verb	Adverb
fish joint	Yes	No	No	No
butt joint	Yes	No	No	No

As nouns, butt joint is a hypernym of fish joint; that is, butt joint is a word with a broader meaning than fish joint:

fish joint: a butt joint formed by bolting fish plates to the sides of two rails or beams
butt joint: a joint made by fastening ends together without overlapping

Other hypernyms of fish joint include butt.

fish joint (noun)	butt joint (noun)
a butt joint formed by bolting fish plates to the sides of two rails or beams	a joint made by fastening ends together without overlapping