1A face like that of a monkey; an amusing or funny face.
2Caribbean informal A grimace, especially one intended to frighten, or made by a child as a sign of disrespect or annoyance.
3US A freshwater mussel, Quadrula metanevra (family Unionidae), with a yellow to light brown shell, found in medium to large rivers in parts of the United States. Also (with distinguishing word): any other mussel of this genus.
4US dialect The barn owl, Tyto alba.
Late 16th century; earliest use found in Thomas Nashe (d. c1601), writer. From monkey + face.