The correct option is
C Cowardice
The word 'grit' indicates strength of character, courage and resolve.
Option A, anxiety indicates a feeling of nervousness, worry or unease about something with an uncertain outcome.
Option B, cowardice refers to lack of bravery.
Option C, impatience indicates irritability or restlessness.
Option D, perseverance refers to persistence in doing something despite difficulty or delay in achieving success.
Thus, according to the meaning, the word 'cowardice' is the most different in meaning from the word 'grit'.