The story
They were introduced into fluid dynamics by Osbourne Reynolds (1895) and named by J. Kampé de Fériet (1934, 1935, 1949).
Etymology from Wiktionary, CC BY-SA 4.0.
Reynolds operator
Today it means: A mathematical operator given by averaging something over a group action, satisfying a set of properties called Reynolds rules, and having applications in fluid dynamics and invariant theory. Full definition →