Webster's Revised Unabridged Dictionary · 1913

Lightweight

Lightweight (līt"wāt`) , noun

One of less than average weight;
In boxing, wrestling, etc., one weighing not more than 133 pounds (U. S. amateur rules 135 pounds, Eng. 140 pounds).
2.
A person of small importance or mental ability, especially one who is unimportant but cheeky and presumptuous. [Colloquial, Chiefly United States]
3.
a wrestler who weighs 139-154 pounds.

Lightweight , adjective

1.
Light in weight, as a coin; specif., applied to a man or animal who is a lightweight.
2.
made of thin cloth, of relatively little weight; -- of clothing or fabrics; as, lightweight fabrics.