Definitions

1. noun

a fixed, usually rigid, expression of the face, especially one of pain, fear, or surprise, as in a grimace

“The patient’s face was frozen in a rictus of pain after the surgery.”

2. noun

a death’s-head moth, especially Acherontia atropos, which is often found in the body of a corpse

“The rictus of the moth was a macabre sight on the deceased’s face.”