Lightweight

Part of speech: noun (n.)

1. In boxing, wrestling, etc., one weighingnot more than 133 pounds (U. S. amateur rules 135 pounds, Eng. 140 pounds).

2. A person of small impotance or mental ability. [Colloq., Chiefly U. S.]

Part of speech: adjective (a.)

Light in weight, as a coin; specif., applied to a man or animal who is a lightweight.