Giving form or shape; having the power of giving form; plastic; shaping; molding; determining: as, the formative yolk of an egg, which changes into an embryo; a formative process.Pertaining to formation or development; related to the fixation of or growth into form or order: as, the formative period of youth or of a nation; formative experiments.In grammar, serving to form; determining grammatical form or character as a part of speech or derivative; inflectional: as, a formative termination.n. In grammar, a formative element of a word; that which serves to give grammatical form; an addition to or modification of a root or crude form, giving it special character.