Anatomy. a muscle that stretches or tightens some part of the body.
Mathematics. a mathematical entity with components that change in a particular way in a transformation from one coordinate system to another.
(anatomy) any muscle that can cause a part to become firm or tense
(maths) a set of components, functions of the coordinates of any point in space, that transform linearly between coordinate systems. For three-dimensional space there are 3r components, where r is the rank. A tensor of zero rank is a scalar, of rank one, a vector