The Collaborative International Dictionary of English v.0.48:

Motionless \Mo"tion*less\, a.
   Without motion; being at rest.
   [1913 Webster]

WordNet (r) 3.0 (2006):

motionless
    adj 1: not in physical motion; "the inertia of an object at
           rest" [syn: inactive, motionless, static, still]

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "motionless":
   at a standstill, at anchor, contemplative, dead-still, do-nothing,
   dormant, fixed, idle, immobile, immotile, immotive, immovable,
   inactive, inert, irremovable, laissez-aller, laissez-faire,
   meditative, moveless, neuter, neutral, out of commission,
   paralytic, paralyzed, passive, procrastinating, quiescent,
   quietist, quietistic, riding at anchor, sedentary, stagnant,
   stagnating, standpat, static, stationary, statuelike, steadfast,
   still, stock-still, unactive, unemployed, unmovable, unmoved,
   unmoving, vegetable, vegetative