rumen vs first stomach

rumen and first stomach both are nouns.

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

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

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

rumen (noun)	first stomach (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