first stomach vs rumen

first stomach and rumen both are nouns.

Word	Noun	Adjective	Verb	Adverb
first stomach	Yes	No	No	No
rumen	Yes	No	No	No

As nouns, first stomach and rumen are synonyms defined as:

first stomach and rumen: the first compartment of the stomach of a ruminant; here food is collected and returned to the mouth as cud for chewing

first stomach (noun)	rumen (noun)
the first compartment of the stomach of a ruminant; here food is collected and returned to the mouth as cud for chewing	the first compartment of the stomach of a ruminant; here food is collected and returned to the mouth as cud for chewing