unconquerable

un- +‎ conquerable

unconquerable (not comparable)

1. Not conquerable; indomitable.
   • 1886 October – 1887 January, H[enry] Rider Haggard, She: A History of Adventure, London: Longmans, Green, and Co., published 1887, OCLC 1167497017:

     "Be careful when power comes to thee also, lest thou too shouldst smite in thine anger or thy jealousy, for unconquerable strength is a sore weapon in the hands of erring man."

• unconquerable in The Century Dictionary, New York, N.Y.: The Century Co., 1911
• unconquerable in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913