A unit of mass. In the US, 1 ton = 2000 lb. In the UK, 1 ton = 2240 lb. Called a long ton in the US. Thesaurus Antonyms Related Words Synonyms Legend: Switch to new thesaurus . Noun: 1. ton - a United States unit of weight equivalent to 2000 pounds. net ton, short ton. avoirdupois unit - any of the units of the avoirdupois system of weights