The police discovered a stash of cash of unknown origin.
Tips
history
From Zhou Mi's 《癸辛杂识》 (Miscellanea of the Guixin Era, Southern Song): 雇一婢，来历不明 - describing a hired maid 'of obscure background.' The phrase has kept the same suspicious tone since.
usage
Nearly always precedes a noun: 来历不明的人 (a shady person), 来历不明的包裹 (a suspicious package), 来历不明的钱 (dodgy money). The implication is not neutral - it signals 'best avoided.'
