between Look up between at Dictionary.com
O.E. betweonum, from bi- "by" + tweonum dat. pl. of *tweon "two each" (cf. Goth. tweih-nai "two each"). Horace Walpole's playful coinage betweenity (1760) is a useful word. Between a rock and a hard place is from 1940s, originally cowboy slang.