expression, godan verb (-su)
forfeit a pawned article
Used when a pawned item is lost because the redemption period has expired. The expression is specific to pawnshop contexts.
期限までに返済できず、質草を流してしまった。
I couldn't repay by the deadline and ended up forfeiting the pawned item.
Compound of 質草 (pawned article) + を + 流す (to let flow, to forfeit). The verb 流す here carries the sense of letting something go or losing it.