for the etymology of the -logy root

word-forming element meaning "a speaking, discourse, treatise, doctrine, theory, science," from Medieval Latin -logia, French -logie, and directly from Greek -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')."