The Collaborative International Dictionary of English v.0.48:
Canthus \Can"thus\, n.; pl. Canthi. [NL., fr. Gr. ?.] (Anat.) The corner where the upper and under eyelids meet on each side of the eye. [1913 Webster]WordNet (r) 3.0 (2006):
canthus n 1: either of the corners of the eye where the upper and lower eyelids meet