ˈren ə ldz- noun
Usage: usually capitalized R
Etymology: after Osborne Reynolds died 1912 English physicist
: an abstract number characteristic of the flow of a fluid in a pipe or past an obstruction used especially in the testing of scale models of airplanes in a wind tunnel : the ratio of the product of the density of the fluid, the flow velocity, and a characteristic linear dimension of the body under observation to the coefficient of absolute viscosity