The Collaborative International Dictionary of English v.0.48:

Limitless \Lim"it*less\, a.
   Having no limits; unbounded; boundless. --Davies (Wit's
   Pilgr.).
   [1913 Webster]

WordNet (r) 3.0 (2006):

limitless
    adj 1: without limits in extent or size or quantity; "limitless
           vastness of our solar system" [syn: illimitable,
           limitless, measureless]
    2: having no limits in range or scope; "to start with a theory
       of unlimited freedom is to end up with unlimited despotism"-
       Philip Rahv; "the limitless reaches of outer space" [syn:
       unlimited, limitless] [ant: limited]
    3: seemingly boundless in amount, number, degree, or especially
       extent; "unbounded enthusiasm"; "children with boundless
       energy"; "a limitless supply of money" [syn: boundless,
       unbounded, limitless]

Moby Thesaurus II by Grady Ward, 1.0:

145 Moby Thesaurus words for "limitless":
   a hog for, absolute, acquisitive, all-comprehensive, all-devouring,
   all-inclusive, all-knowing, all-powerful, all-seeing, all-wise,
   almighty, avaricious, avid, bottomless, boundless, changeless,
   countless, coveting, covetous, creating, creative, devouring,
   endless, enormous, esurient, eternal, eternally the same,
   everlasting, exhaustless, extending everywhere, extensive, full,
   glorious, gluttonous, gobbling, good, grabby, grasping, greedy,
   hallowed, highest, hoggish, holy, illimitable, illimited,
   immeasurable, immense, immortal, immutable, incalculable,
   incessant, incomprehensible, indefinite, inexhaustible, infinite,
   infinitely continuous, innumerable, insatiable, insatiate,
   interminable, interminate, just, loving, luminous, majestic,
   making, measureless, mercenary, merciful, miserly, money-hungry,
   money-mad, myriad, no end of, no strings, numberless, numinous,
   omnipotent, omnipresent, omniscient, omnivorous, one, open,
   overgreedy, perfect, permanent, perpetual, piggish, plenary,
   quenchless, radiant, rapacious, ravening, ravenous, sacred,
   shaping, shoreless, slakeless, sordid, sovereign, sumless, supreme,
   swinish, termless, timeless, ubiquitous, unappeasable, unappeased,
   unbound, unbounded, unceasing, unchanging, uncircumscribed,
   unconditional, unconditioned, unconfined, undefined, unending,
   unequivocal, unfathomable, universal, unlimited, unmeasurable,
   unmeasured, unnumbered, unplumbed, unqualified, unquenchable,
   unrestrained, unrestricted, unsated, unsatisfied, unslakeable,
   unslaked, untold, vast, venal, voracious, wide-open, without bound,
   without end, without limit, without measure, without number,
   without strings