Key: "S:" = Show Synset (semantic) relations, "W:" = Show Word (lexical) relations
Display options for sense: (gloss) "an example sentence"
Noun
S: (n) principal axis, optic axis (a line that passes through the center of curvature of a lens so that light is neither reflected nor refracted) "in a normal eye the optic axis is the direction in which objects are seen most distinctly"