ex·pres·siv·i·ty \ˌekˌspreˈsivəd.ē, -vətē, -i\noun (-es) Etymology: International Scientific Vocabulary expressive + -ity; originally formed as German expressivität 1.: the relative capacity of a gene to modify the organism of which it is a part — compare penetrance 2.[expressive + -ity]: the quality of being expressive < works in which intellectual interest … is in perfect balance with expressivity — Edward Cushing >