expression /ikspresh″ən/ [L, exprimere, to express] , 1. the indication of a physical or emotional state through facial appearance or vocal intonation. 2. the act of pressing or squeezing to expel something, such as milk from the breast when lactating or the fetus from the uterus by exertion of pressure on the abdominal wall. 3. (in genetics) the detectable effect or appearance in the phenotype of a particular trait or condition. See also expressivity. −express, v.
