What does abomasum or abomasus mean?
The definition of abomasum and abomasus
Ab`o*ma”sum, Ab`o*ma”sus, n.
Etym: [NL., fr. L. ab + omasum (a Celtic word.] (Anat.)

The fourth or digestive stomach of a ruminant, which leads from the third stomach omasum. See Ruminantia.