(combat sports) 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.

Lacking in earnestness, ability, or profundity / Having less than average weight / Lacking in strength / (computing) Having a small footprint or performance impact

(transitive) To reduce the amount or weight of.

plural of lightweight

The quality or condition of being lightweight.