isohyet
noun
iso·hy·et ˌī-sō-ˈhī-ət 
: a line on a map or chart connecting areas of equal rainfall
isohyetal
ˌī-sō-ˈhī-ə-təl
adjective 
Example Sentences
Recent Examples on the Web Powell had drawn an isohyet, a line connecting areas that experience equal volumes of annual rainfall. 
Johnforristerross, Longreads, 2 July 2018 The man who had previously limited himself to describing the topographic and geologic formations of the western lands had now waded directly into populist politics, driven by isohyets and tables of rainfall-per-acre statistics. Johnforristerross, Longreads, 2 July 2018
Johnforristerross, Longreads, 2 July 2018 The man who had previously limited himself to describing the topographic and geologic formations of the western lands had now waded directly into populist politics, driven by isohyets and tables of rainfall-per-acre statistics. Johnforristerross, Longreads, 2 July 2018 Word History
Etymology
International Scientific Vocabulary is- + Greek hyetos rain, from hyein to rain; probably akin to Tocharian B swese rain
First Known Use
1899, in the meaning defined above