The Collaborative International Dictionary of English v.0.48:

Unending \Unending\
   See ending.

WordNet (r) 3.0 (2006):

unending
    adj 1: continuing forever or indefinitely; "the ageless themes
           of love and revenge"; "eternal truths"; "life
           everlasting"; "hell's perpetual fires"; "the unending
           bliss of heaven" [syn: ageless, aeonian, eonian,
           eternal, everlasting, perpetual, unending,
           unceasing]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "unending":
   ageless, amaranthine, articulated, catenated, ceaseless, coeternal,
   concatenated, connected, constant, continual, continued,
   continuing, continuous, cyclical, dateless, direct, endless,
   eternal, eterne, ever-being, ever-durable, ever-during,
   everlasting, everliving, featureless, gapless, immediate,
   immemorial, immortal, incessant, indestructible, infinite,
   interminable, joined, jointless, linked, monotonous, never-ceasing,
   never-ending, nonstop, nonterminating, nonterminous, olamic,
   perdurable, perennial, periodic, permanent, perpetual, recurrent,
   repetitive, round-the-clock, running, seamless, sempiternal,
   serried, smooth, stable, steady, straight, timeless,
   twenty-four-hour, unbroken, unceasing, undifferentiated, uniform,
   unintermitted, unintermittent, unintermitting, uninterrupted,
   unrelieved, unremitting, unstopped, without end