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Houghton Mifflin

pto·sis  audio  (tss) KEY 

NOUN:
pl. pto·ses  (-sz) KEY 
Abnormal lowering or drooping of an organ or a part, especially a drooping of the upper eyelid caused by muscle weakness or paralysis.

ETYMOLOGY:
Greek ptsis, fall, from piptein, pt-, to fall; see pet- in Indo-European roots

OTHER FORMS:
ptotic  (-tk) KEY (Adjective)


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