noun

1. Someone who sleeps.

   “I'm a light sleeper: I get woken up by the smallest of sounds.”

2. That which lies dormant, as a law.

3. A spy, saboteur, or terrorist who lives unobtrusively in a community until activated by a prearranged signal; may be part of a sleeper cell.

Synonyms: sleeper hit

verb

1. To mark a calf by cutting its ear.