The synonym of DISCOMFIT is: 

Concept: Words that have similar meanings and in the sentence replacing one with another do not change the meaning of the sentence are known as synonyms.

• Words which contradict each other are referred to as antonyms. 
• According to the question we need to find the synonym of discomfort.
• Discomfort means not feeling good or feeling uneasy.
• Option A: Litigate means taking legal action.
• Option B: Ease means absence of hard work or presence of comfort.
• Option C: Conflict means argument or disagreement.
• Option D: Frustrate means a situation of uneasiness and confusion.
• Therefore the synonym of the given word is Frustrate.

Hence, option D is the correct answer.