KanjiJLPT N3
Settle (debt, etc.)

settle (debt, etc.), relieve (burden), finish, come to an end, excusable, need not

Mnemonic

A storm wipes out the village's debt records. The elders decree uniformity: everyone must settle what they owe from memory, paying their exact share. The storm erased the books, but uniformity in honest repayment will settle every account.
Additional thoughts
Picture a storm destroying ledgers, then villagers lining up uniformly to settle debts on the honor system. The chaos of the storm meets the order of uniformity — settling is what resolves both.
Quick recall
A storm erases the books, but uniformity in repayment will settle every debt.

Details

The keyword for 済 is settle. This kanji conveys the idea of settling or finishing something, particularly in the sense of completing an obligation such as paying off a debt or resolving a matter. It carries the nuance of bringing something to a satisfactory conclusion, ensuring that all accounts are cleared and nothing remains outstanding. By extension, it can also refer to relief or salvation, as in rescuing someone from a difficult situation, and is commonly associated with economic or financial matters.
On'yomi
さい、せい
Kun'yomi
す.む、-ず.み、-ずみ、す.まない、す.ます、-す.ます、すく.う、な.す、わたし、わた.る