The Collaborative International Dictionary of English v.0.48:

Formless \Form"less\, a.
   Shapeless; without a determinate form; wanting regularity of
   shape. -- Form"less*ly, adv. -- Form"less*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

formless
    adj 1: having no definite form or distinct shape; "amorphous
           clouds of insects"; "an aggregate of formless particles";
           "a shapeless mass of protoplasm" [syn: amorphous,
           formless, shapeless]
    2: having no physical form; "belief in a world filled
       with...formless but often malevolent beings"

Moby Thesaurus II by Grady Ward, 1.0:

113 Moby Thesaurus words for "formless":
   aberrant, abnormal, abundant, aimless, amorphic, amorphous,
   anarchic, anomalistic, anomalous, baggy, blobby, blurred, blurry,
   capricious, casual, chaotic, characterless, confused, copious,
   desultory, deviative, different, diffuse, diffusive,
   disarticulated, discontinuous, disjunct, disordered, disorderly,
   dispersed, disproportionate, divergent, eccentric, effusive,
   erratic, extravagant, exuberant, featureless, fecund, fitful,
   frivolous, fuzzy, gratuitous, gushing, gushy, haphazard, hazy,
   heteroclite, heteromorphic, hit-or-miss, immethodical, inchoate,
   incoherent, indecisive, indefinite, indeterminate, indiscriminate,
   inform, irregular, kaleidoscopic, lumpen, meaningless, misshapen,
   misty, nondescript, nonsymmetrical, nonsystematic, nonuniform,
   obscure, orderless, overflowing, planless, pleonastic, prodigal,
   productive, profuse, profusive, prolific, promiscuous, random,
   redundant, reiterative, repetitive, senseless, shapeless,
   spasmodic, sporadic, straggling, straggly, stray, straying,
   subnormal, superabundant, systemless, tautologous, teeming,
   unarranged, unclassified, unclear, undefined, undirected, ungraded,
   unjoined, unmethodical, unnatural, unordered, unorganized,
   unsorted, unsymmetrical, unsystematic, ununiform, vague,
   wandering