lightweight

Short definition from Wiktionary

Noun

1. 1
   A particular weight class, or member of such, as prescribed by the rules, between that of the heavier welterweight and the lighter featherweight. See Wikipedia for the specifics of each sport.
2. 2
   A particular weight category as prescribed by the rules, separate from an open or heavyweight class.
3. 3
   A competitive weight division as prescribed by the rules, between the heavier middleweight and the lighter featherweight.
4. 4
   One of little consequence or ability.
5. 5
   A person who cannot handle their drink; one who gets drunk on very little alcohol.
6. 6
   A person with low endurance.
7. 7
   A political candidate with little chance of winning.

Adjective

1. 1
   Lacking in earnestness, ability, or profundity.
2. 2
   Having less than average weight.
3. 3
   Lacking in strength.
4. 4
   Having a small footprint or performance impact.

Verb

1. 1
   To reduce the amount or weight of.