-gnathycomb. form

Primary stress is attracted to the syllable immediately preceding this combining form and vowels may be reduced accordingly; see e.g. 
prognathy n.Origin: A borrowing from Greek, combined with an English element. Etymons: Greek γνάθος  , -y suffix3.
Etymology:  <  ancient Greek γνάθος jaw (see -gnath comb. form) + -y suffix3. Compare German -gnathie  . Compare -gnathism comb. form.Found in a very small number of formations in the late 19th cent., e.g. mesognathy n., prognathy n.
 Chiefly 
Physical Anthropology.
This is a new entry (OED Third Edition, November 2010; most recently modified version published online December 2018).