E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Arithmetic in which the base of the notation is 2 instead of 10. The unit followed by a cipher signifies two, by another unit it signifies three, by two ciphers it signifies four, and so on. Thus, 10 signifies two, 100 signifies four; while 11 signifies 3, ete.