狱 (yù) is a bound morpheme (b.f.) that always appears as part of a compound word. Its core meaning is 'prison' or 'jail', as in 监狱 (prison), 地狱 (hell), and 越狱 (to break out of prison). It can also refer to legal cases in compounds like 狱讼 (litigation) or 冤狱 (unjust verdict). You cannot use 狱 alone as a standalone word; you must pair it with another morpheme.