abomasum vs fourth stomach

abomasum and fourth stomach both are nouns.

Word	Noun	Adjective	Verb	Adverb
abomasum	Yes	No	No	No
fourth stomach	Yes	No	No	No

As nouns, abomasum and fourth stomach are synonyms defined as:

abomasum and fourth stomach: the fourth compartment of the stomach of a ruminant; the one where digestion takes place

abomasum (noun)	fourth stomach (noun)
the fourth compartment of the stomach of a ruminant; the one where digestion takes place	the fourth compartment of the stomach of a ruminant; the one where digestion takes place