Transvestite

Noun

1. A person who sometimes wears clothes traditionally worn by and associated with the opposite sex; typically a male who cross-dresses occasionally by habit or personal choice.

   "Even though Steven used to dress up in his sister's clothes, it still came as a surprise he ended up as a transvestite."

2. A person, typically a heterosexual male, who compulsively seeks and derives paraphilic sexual arousal from cross-dressing, especially if the urges and behavior cause the patient distress or social impairment.
3. An animal that engages in sexual mimicry.