During a talk today by Sid Redner, the question came up as to the origin of the expression “master equation.” According to the Oxford English Dictionary, the first such use of the term was given in by A. Nordsieck et al. in Physica 7, p. 353, 1940
The required probability of an energy distribution will be a function of the numbers ni and of x, which we will denote by W(n1, n2,..; x). From this function W one can find all other distribution functions… When the probabilities of the elementary processes are known, one can write down a continuity equation for W, from which all other equations can be derived and which we will call therefore the “master” equation.
Damn, I thought it was named after “The Master”, Dr Who’s nemisis in the TV show. Um, that joke might only make sense to geeks from countries that get a lot of British TV….