word-forming element meaning "billion" (U.S.) in the metric system, 1947, formed arbitrarily from Greek gigas "giant" (see giant).
ton n.1
"measure of weight," late 14c. The quantity necessary to fill a tun or cask of wine, thus identical to tun (q.v.). The spelling difference became firmly established 18c. Ton of bricks in the colloquial figurative sense of what you come down on someone like is from 1884.