From Wiktionary, the free dictionary
From ថយ (thɑɑy, “to retreat; to be reduced”) with prefixed bVN- (causative).
បន្ថយ • (bɑnthɑɑy) (abstract noun ការបន្ថយ)
- to cause to retreat, withdraw (as an army), pull back
- to decrease, to lessen, to reduce, to shorten, to diminish, to weaken, to lower