|the direction in a uniaxial crystal or one of the two directions in a biaxial crystal along which a ray of unpolarized light may pass without undergoing double refraction|
|a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.|
|a gadget; dingus; thingumbob.|
optic axis n.
The line connecting the anterior and the posterior poles of the eye.