宜 is a bound form (黏着语素) that cannot stand alone — it always appears as part of disyllabic words. As a morpheme, it carries the core meaning of 'suitable' or 'appropriate' (as in 适宜 shìyí 'suitable' or 宜人 yírén 'pleasant'), and in negative structures like 不宜 bùyí it functions like a modal meaning 'should not' or 'ought not', similar to 应该 in the negative. The specific sense depends on the compound.