The Collaborative International Dictionary of English v.0.48:

Unconquerable \Unconquerable\
   See conquerable.

The Collaborative International Dictionary of English v.0.48:

Unconquerable \Un*con"quer*a*ble\, a.
   Not conquerable; indomitable. -- Un*con"quer*a*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unconquerable
    adj 1: not capable of being conquered or vanquished or overcome;
           "a tribute to his courage...and his unconquerable will"-
           R.E.Danielson; "faced unconquerable difficulties" [ant:
           conquerable]
    2: incapable of being surmounted or excelled; "insuperable
       odds"; "insuperable heroes" [syn: insuperable,
       unconquerable]

Moby Thesaurus II by Grady Ward, 1.0:

88 Moby Thesaurus words for "unconquerable":
   assiduous, constant, continuing, diligent, dogged, enduring,
   faithful, immutable, impassable, impenetrable, impregnable,
   inalterable, incontestable, indefatigable, indomitable,
   industrious, inexpugnable, insistent, insuperable, insurmountable,
   invincible, inviolable, invulnerable, irresistible, lasting, loyal,
   never-tiring, obstinate, overpowering, overwhelming, patient,
   patient as Job, permanent, perseverant, persevering, persistent,
   persisting, pertinacious, plodding, plugging, preoccupied, proof,
   rapt, relentless, resistant, resistless, resolute, secure,
   sedulous, single-minded, sleepless, slogging, stable, steadfast,
   steady, stubborn, tenacious, tight, tireless, unabating,
   unassailable, unbeatable, undaunted, undefeatable, undiscouraged,
   undrooping, unfailing, unfaltering, unflagging, unflinching,
   unintermitting, uninterrupted, unnodding, unrelaxing, unrelenting,
   unremitting, unsleeping, unsubduable, unsurmountable, unswerving,
   untiring, unwavering, unwearied, unwearying, unwinking, unyielding,
   utterly attentive, weariless