the female of a pair of twin calves of unlike sex that is imperfectly developed and sterile, probably due to the influence of the male hormones of its twin during development in the uterus
Word origin
C17: of uncertain origin
freemartin in American English
(ˈfriˌmɑrtən)
noun
an imperfectly developed female calf, usually sterile, born as the twin of a male