Definition of red-mouthed in US English:

red-mouthed

adjective

  • 1In the names of animals (especially fish): having red coloration around the mouth.

  • 2More generally: that has or is characterized by a red mouth.

Origin

Mid 18th century; earliest use found in John Hill (bap. 1714, d. 1775), physician and actor. From red + mouthed.