noun

1. ☆ the basic monetary unit of the U.S., equal to 100 cents: symbol, $: certain other countries, as Ecuador, Panama, El Salvador, and the Marshall Islands, have officially adopted this monetary unit
2. any of the standard monetary units of various other countries, as of Australia, Barbados, and Canada
3. the Mexican peso
4. a coin or piece of paper money of the value of a dollar
5. Obsolete a Spanish coin (piece of eight) used in American Revolutionary times

Etymology: LowG & Fl daler < Ger thaler (now taler), contr. < Joachimsthaler, coin made (orig. in 1519) at (St.) Joachimstal, Bohemia < (St.) Joachim + thal, tal, valley: see dale