a method of transforming a text in order to conceal its meaning; a code
a message in code
a key to such a code
a combination of symbolic letters, esp a monogram
archaic = zero1 (1)
somebody who or something that has no worth or influence; a nonentity
‘There I shall see mine own figure.’ ‘Which I take to be either a fool or a cipher’ — Shakespeare
any of the Arabic numerals
[Middle English from early French cifre via medieval Latin from Arabic ṣifr empty, cipher, zero]