The Collaborative International Dictionary of English v.0.48:

Unremitting \Un`re*mit"ting\, a.
   Not remitting; incessant; continued; persevering; as,
   unremitting exertions. --Cowper. -- Un`re*mit"ting*ly, adv.
   -- Un`re*mit"ting*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unremitting
    adj 1: uninterrupted in time and indefinitely long continuing;
           "the ceaseless thunder of surf"; "in constant pain";
           "night and day we live with the incessant noise of the
           city"; "the never-ending search for happiness"; "the
           perpetual struggle to maintain standards in a democracy";
           "man's unceasing warfare with drought and isolation";
           "unremitting demands of hunger" [syn: ceaseless,
           constant, incessant, never-ending, perpetual,
           unceasing, unremitting]

Moby Thesaurus II by Grady Ward, 1.0:

185 Moby Thesaurus words for "unremitting":
   abiding, ageless, ardent, articulated, assiduous, catenated,
   ceaseless, changeless, chattering, coeternal, concatenated,
   connected, constant, continual, continued, continuing, continuous,
   cyclical, dateless, diligent, direct, dogged, endless, enduring,
   energetic, eternal, eterne, ever-being, ever-durable, ever-during,
   everlasting, everliving, faithful, featureless, fervent, gapless,
   hard, hardworking, immediate, immemorial, immutable, inalterable,
   incessant, incommutable, inconvertible, indefatigable,
   indefeasible, indestructible, indomitable, industrious, inert,
   infinite, insistent, insusceptible of change, interminable,
   intransmutable, invariable, invincible, irretrievable,
   irreversible, irrevocable, joined, jointless, laborious, lasting,
   linked, loyal, machine gun, monotonous, never idle, never-ceasing,
   never-ending, never-tiring, noble, nonreturnable, nonreversible,
   nonstop, nonterminating, nonterminous, obstinate, olamic,
   oscillating, patient, patient as Job, perdurable, perennial,
   periodic, permanent, perpetual, perseverant, persevering,
   persistent, persisting, pertinacious, plodding, plugging,
   preoccupied, pulsating, rapid, rapt, recurrent, regular,
   relentless, remaining, repeated, repetitive, resolute, reverseless,
   round-the-clock, running, seamless, sedulous, sempiternal, serried,
   single-minded, sleepless, slogging, smooth, stable, staccato,
   staying, steadfast, steady, sticking, straight, strenuous,
   stubborn, stuttering, sustained, tenacious, timeless, tireless,
   twenty-four-hour, unabating, unalterable, unalterative, unaltered,
   unbroken, unceasing, unchangeable, unchanged, unchanging,
   unconquerable, undaunted, undeflectable, undeviating,
   undifferentiated, undiscouraged, undrooping, undying, unending,
   unfailing, unfaltering, unflagging, unflinching, uniform,
   unintermitted, unintermittent, unintermitting, uninterrupted,
   unmodifiable, unnodding, unrelaxing, unrelenting, unrelieved,
   unrestorable, unreturnable, unsleeping, unsparing, unstopped,
   unsusceptible, unswerving, untiring, unvariable, unvarying,
   unwavering, unwearied, unwearying, unwinking, utterly attentive,
   vehement, vibrating, weariless, without end, zealous