(Originally) a person, typically a woman, who performs a sexual role or function mechanically and without feeling; (later usually) a person characterized as vigorous, unremitting, and insatiable in his or her pursuit and performance of sex.
Origin
1920s.
Definition of sex machine in US English:
sex machine
noun
(Originally) a person, typically a woman, who performs a sexual role or function mechanically and without feeling; (later usually) a person characterized as vigorous, unremitting, and insatiable in his or her pursuit and performance of sex.