butt-welding vs welding

butt-welding and welding both are nouns.

Word	Noun	Adjective	Verb	Adverb
butt-welding	Yes	No	No	No
welding	Yes	No	No	No

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

butt-welding: creating a butt joint by welding
welding: fastening two pieces of metal together by softening with heat and applying pressure

butt-welding (noun)	welding (noun)
creating a butt joint by welding	fastening two pieces of metal together by softening with heat and applying pressure