The Collaborative International Dictionary of English v.0.48:

Undeclared \Undeclared\
   See declared.

WordNet (r) 3.0 (2006):

undeclared
    adj 1: not announced or openly acknowledged; "fighting an
           undeclared war" [ant: declared]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "undeclared":
   implicit, implied, inferred, silent, understood, unexpressed,
   unmentioned, unproclaimed, unpronounced, unpublished, unrecorded,
   unsaid, unspoken, unsung, untalked-of, untold, unuttered, unvoiced,
   unwritten, wordless