Common compounds: 赎回 (shúhuí, to redeem/buy back), 赎罪 (shúzuì, to atone for sins), 赎金 (shújīn, ransom money). Can be used literally (paying ransom) or figuratively (atoning).
memory
The left radical 贝 (bèi) means 'shell/money' — you pay money to buy someone's freedom back. The right side 卖 relates to selling/trading.