The Collaborative International Dictionary of English v.0.48:

Cater-cornered \Ca"ter-cor`nered\, a. [Cf. Cater to cut
   diagonally.]
   Diagonal. [Colloq.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

cater-cornered
    adj 1: slanted across a polygon on a diagonal line; "set off in
           a catty-corner direction across the vacant lot" [syn:
           catacorner, cata-cornered, catercorner, cater-
           cornered, catty-corner, catty-cornered, kitty-
           corner, kitty-cornered]