Final answer:
The quote "I thank whatever gods may be / For my unconquerable soul" best supports the meaning of 'Invictus' as 'unconquered,' highlighting the poem's theme of unwavering strength.
Step-by-step explanation:
The title word "Invictus" in the poem by William Ernest Henley most likely means 'unconquered' or 'undefeated'. To support this interpretation of "Invictus" meaning unwavering strength despite adversity, the quote that best supports the context of the poem is "I thank whatever gods may be / For my unconquerable soul" (Lines 3-4). This line directly refers to an unconquerable soul, which aligns with the idea of being undefeated or invincible as suggested by the title.