What is "stereo-"

Stereo- \Ste"re*o-\ [Gr. stereo`s solid. See Stare to gaze.] A combining form meaning solid, hard, firm, as in stereo-chemistry, stereography.

before vowels stere-, word-forming element meaning "solid, firm; three-dimensional; stereophonic," from comb. form of Greek stereos "solid," from PIE *ster- (1) "stiff, rigid, firm, strong" (cognates: Greek steresthai "be deprived of," steira "sterile," sterphnios "stiff, rigid," sterphos "hide, skin;" Latin sterilis "barren, unproductive;" Sanskrit sthirah "hard, firm," starih "a barren cow;" Persian suturg "strong;" Lithuanian storas "thick," stregti "to become frozen;" Old Church Slavonic strublu "strong, hard," sterica "a barren cow," staru "old" (hence Russian stary "old"); Gothic stairo "barren;" Old Norse stirtla "a barren cow," Old English starian "to stare," stearc "stiff, strong, rigid," steorfan "to die," literally "become stiff," styrne "severe, strict").

pre. 1 (non-gloss definition: Forming words relating to the solid, the three-dimensional.) 2 (non-gloss definition: Specifically, forming words relating to the binocular contribution to three-dimensional vision.) 3 (non-gloss definition: Forming words relating to the solid, the hard.)