n. In anatomy, one of several muscles which tighten a part, or make it tense, or put it upon the stretch: differing from an extensor in not changing the relative position or direction of the axis of the part: opposed to laxator.n. In mathematics, the modulus of a quaternion; the ratio in which it stretches the length of a vector.In anatomy, noting certain muscles whose function is to render fasciæ or other structures tense.