"pertaining to the abdomen, ventral," 1550s, from medical Latin abdominalis, from abdomen (genitive abdominis); see abdomen. As a noun, in modern use, "abdominal muscle;" earlier as a fish of the order including carp, salmon, herring (1835), so called for their ventral fins. Related: Abdominally. English in 17c. had abdominous "big-bellied."