reducer vs pipe fitting

reducer and pipe fitting both are nouns.

Word	Noun	Adjective	Verb	Adverb
reducer	Yes	No	No	No
pipe fitting	Yes	No	No	No

As nouns, pipe fitting is a hypernym of reducer; that is, pipe fitting is a word with a broader meaning than reducer:

reducer: pipefitting that joins two pipes of different diameter
pipe fitting: fitting consisting of threaded pieces of pipe for joining pipes together

Other hypernyms of reducer include pipefitting.

reducer (noun)	pipe fitting (noun)
pipefitting that joins two pipes of different diameter	fitting consisting of threaded pieces of pipe for joining pipes together
a substance capable of bringing about the reduction of another substance as it itself is oxidized; used in photography to lessen the density of a negative or print by oxidizing some of the loose silver