noun

• (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.
• (rowing) A particular weight category as prescribed by the rules, separate from an open or heavyweight class.
• (weightlifting) A competitive weight division as prescribed by the rules, between the heavier middleweight and the lighter featherweight.
• (by extension) A person with low endurance.

adj

• (computing) Having a small footprint or performance impact.

verb

• (transitive) To reduce the amount or weight of.
  "By extending the producer’s responsibility to the product’s disposal (its post-consumer life), issues previously outside the business calculus become of paramount importance. Because a producer knows it will have to bear the cost of collecting and valorizing the product, it must manage a new set of business matters. Can the packaging be lightweighted? Are the materials all recyclable?"