Sentence:  Judge, O you gods, how dearly Caesar loved him! / This was the most <WSD>unkindest</WSD> cut of all; / For when the noble Caesar saw him stab, / Ingratitude, more strong than traitors' arms, / Quite vanquish'd him: then burst his mighty heart; 
Meaning of the word marked with <WSD> tags:  Lacking kindness, sympathy, benevolence, gratitude, or similar; cruel, harsh or unjust; ungrateful. (From mid-14thC.)