"science of bodily humors," 1787, from French or German hygrologie, which are earlier, or from hygro- "wet, moist; moisture" + -logy.
Entries linking to hygrology
hygro-
word-forming element meaning "wet, moist; moisture," from Greek hygros "wet, moist, fluid; weak, soft, flexible." Beekes says possible cognates include Old Norse vokr (accusative vokvan) "moist, wet;" Latin uvidus, udus.
-logy
word-forming element meaning "a speaking, discourse, treatise, doctrine, theory, science," from Greek -logia (often via French -logie or Medieval Latin -logia), from -log-, combining form of legein "to speak, tell;" thus, "the character or deportment of one who speaks or treats of (a certain subject);" from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')." Often via Medieval Latin -logia, French -logie. In philology "love of learning; love of words or discourse," apology, doxology, analogy, trilogy, etc., Greek logos "word, speech, statement, discourse" is directly concerned.