Grammar. the merging, as by historical change in a language, of two or more categories in a specified environment into one, as, in nonstandard English, the use of was with both singular and plural subjects, while in standard English was is used with singular subjects (except for you in ...
Voice has been used as a term to describe the familiar active/passive alternation in many Indo-European languages, but it is also widely used to describe argument increasing/decreasing alternations, such as the so-called middle Voice which refers to reflexive, reciprocal, benefactive, dispositional ...