The Collaborative International Dictionary of English v.0.48:

Wordless \Word"less\, a.
   Not using words; not speaking; silent; speechless. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

wordless
    adj 1: expressed without speech; "a mute appeal"; "a silent
           curse"; "best grief is tongueless"- Emily Dickinson; "the
           words stopped at her lips unsounded"; "unspoken grief";
           "choking exasperation and wordless shame"- Thomas Wolfe
           [syn: mute, tongueless, unspoken, wordless]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "wordless":
   anaudic, aphasic, aphonic, breathless, brief, brusque, close,
   close-lipped, close-tongued, closemouthed, concise, curt, dumb,
   dumbfounded, dumbstricken, dumbstruck, economical of words,
   implicit, implied, inarticulate, indisposed to talk, inferred,
   laconic, mum, mute, quiet, reserved, reticent, short, silent, snug,
   sparing of words, speechless, stricken dumb, tacit, taciturn,
   terse, tight-lipped, tongue-tied, tongueless, uncommunicative,
   undeclared, understood, unexpressed, unloquacious, unmentioned,
   unproclaimed, unpronounced, unpublished, unrecorded, unsaid,
   unspoken, unsung, untalkative, untalked-of, untold, unuttered,
   unvoiced, unwritten, voiceless, word-bound