chosen 1786 as name for U.S. 10 cent coin, from dime "a tenth, tithe" (late 14c.), from O.Fr. disme, from L. decima (pars) "tenth (part)," from decem "ten" (see ten). The verb meaning "to inform" (on someone) is 1960s, from the then-cost of a pay phone call. A dime a dozen "almost
worthless" first recorded 1930. Phrase stop on a dime attested by 1954 (a dime being the physically smallest unit of U.S. currency).
So plentiful as to be valueless. For example, Don't bother to buy one of thesethey're a dime a dozen. The dime was declared the American ten-cent coin in 1786 by the Continental Congress. [First half of 1900s]