IPA: /ˈaɪɡlæs/
KK: /ˈaɪˌɡlæs/
A single lens or a type of glasses that helps people see better.
He put on his eyeglass to read the small print.
Eyeglass is formed from "eye" (from Old English "ēage", meaning the organ of sight) and "glass" (from Old English "glæs", meaning a transparent material). The word "eyeglass" refers to a glass lens used to aid vision, specifically for the eyes.
Think of the 'eye' as the organ of sight and 'glass' as the transparent material that helps you see better. An eyeglass is a glass that aids your eye.