The Collaborative International Dictionary
Hyetology
Hyetology \Hy`e*tol"o*gy\, n. [Gr. ? + rain -logy.] The science which treats of the precipitation of rain, snow, etc. -- Hy`e*to*log"ic*al, a.
Wiktionary
hyetology
n. (context rare archaic English) the scientific study of precipitation.