vest·ed in·ter·est • n. [usu. in sing.] a personal stake or involvement in an undertaking or state of affairs, esp. one with an expectation of financial gain: banks have a vested interest in the growth of their customers. ∎ a person or group having such a personal stake or involvement: the problem is that the authorities are a vested interest. ∎ Law an interest (usually in land or money held in trust) recognized as belonging to a particular person.