The Collaborative International Dictionary of English v.0.48:

Purposeless \Pur"pose*less\, a.
   Having no purpose or result; objectless. --Bp. Hall. --
   Pur"pose*less*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

purposeless
    adj 1: not evidencing any purpose or goal [ant: purposeful]
    2: serving no useful purpose; having no excuse for being;
       "otiose lines in a play"; "advice is wasted words"; "a
       pointless remark"; "a life essentially purposeless";
       "senseless violence" [syn: otiose, pointless,
       purposeless, senseless, superfluous, wasted]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "purposeless":
   aimless, bootless, casual, causeless, designless, desultory,
   discursive, disorganized, driftless, dysteleological, empty,
   feckless, fustian, garbled, good-for-nothing, haphazard,
   hit-or-miss, importless, impotent, inane, indiscriminate,
   ineffective, ineffectual, inexplicable, insignificant, irregular,
   meaningless, mindless, no go, nonconnotative, nondenotative,
   nonsensical, null, of no use, phatic, pointless, promiscuous,
   purportless, rambling, random, scrambled, senseless, stochastic,
   stray, superfluous, unaccountable, unavailing, undirected,
   unhelpful, unmeaning, unmotivated, unorganized, unplanned,
   unprofitable, unpurposed, unsignificant, useless, vacuous,
   wandering, worthless