The correct option is
A Lose
The word 'clinch' refers to confirming or settling a contract or bargain.
Option A, lose refers to failing to win a game or contest.
Option B, clasp refers to grasping something tightly with one's hand.
Option C, deal refers to taking part in commercial trading of a particular commodity.
Option D, seal refers to a thing regarded as a confirmation or guarantee of something.
Thus, according to the meaning, the word 'lose' is the most opposite in meaning from the word 'clinch'.