risus

Risus is a Latin noun meaning laughter. In classical and medieval Latin, it denotes the act or expression of laughing and can appear in descriptions of mirth, jokes, or jovial scenes. It is a masculine noun of the fourth declension; the nominative singular is risus and the genitive singular risūs.

In medical and anatomical terminology the root appears in several forms. The compound risus sardonicus describes a grimacing, sardonic smile caused by sustained contraction of facial muscles; it is a classic sign of tetanus and may appear in other severe neuromuscular conditions or certain poisonings. The term highlights the association between a facial expression and underlying pathology.

The related forms give rise to anatomical terms such as risorius, the muscle that retracts the corner of the mouth during smiling or laughing. The name reflects the Latin origin of laughter.

In modern English, risus is chiefly encountered in scholarly or historical Latin contexts, or within specialized medical phrases such as risus sardonicus. Otherwise, English speakers typically use words such as laughter or smile to convey the general sense.

See also: Laughter; Risorius; Risus sardonicus; Tetanus.