unguessable

English

Etymology

un- +‎ guessable

Adjective

unguessable (comparative more unguessable, superlative most unguessable)

1. Not capable of being guessed.
   • 2001, Simson Garfinkel, Gene Spafford, Web Security, Privacy and Commerce

     Especially bad are "magic words" from computer games, such as xyzzy. These magic words look secret and unguessable, but in fact they are widely known.