What is "penis captivus"

n. The supposed event of a penis trapped by vaginal muscles and unable to withdraw from a vagina during heterosexual intercourse.

Penis captivus is a rare occurrence in intercourse when the muscles in the vagina clamp down on the penis much more firmly than usual (a form of vaginismus), making it impossible for the penis to withdraw from the vagina. According to a 1979 article in the British Medical Journal, this condition was unknown in the twentieth century, but a subsequent letter to the same journal reported an apparent case of penis captivus in 1947. Penis captivus should not be confused with vaginismus, though a relation between the supposed event of penis captivus and the occurrence of vaginismus is assumed in the existing descriptions.