Definition of playfair:
(n) :
(cryptography) an encryption using the Playfair cipher
(n) :
(crosswording) A form of crossword in which some words must be encrypted with a Playfair cipher before being inserted into the grid, and solvers must deduce the codeword and the encrypted clues.
(n) :
A surname.
(n) :
A placename
(n) :
A number of craters in Solar System.
(n) :
A crater in Mars, Solar System.