I'm looking at the Second Pocket Edition of Black's Law Dictionary (ed. Bryan Garner).

rape, n. 1. At common law, unlawful sexual intercourse committed by a man with a woman no his wife through force and against her will. 2. Unlawful sexual activity (esp. intercourse) with a person (usu. a female) without consent and usu. by force or threat of injury.

The first definition is largely historical, since rape (or sexual assault) is typically a statutory crime in the US. The second definition is much more in line with our usage, though it does note that rape usually refers to a woman victim.

Edit: Formatting