Old English glæs "glass; a glass vessel," from Proto-Germanic *glasam "glass" (source also of Old Saxon glas, Middle Dutch and Dutch glas, German Glas, Old Norse gler "glass, looking glass," Danish glar), from PIE root *ghel- (2) "to shine," with derivatives denoting bright colors or materials. The PIE root also is the ancestor of widespread words for gray, blue, green, and yellow, such as Old English glær "amber," Latin glaesum "amber" (which might be from Germanic), Old Irish glass "green, blue, gray," Welsh glas "blue."
Restricted sense of "drinking glass" is from early 13c. and now excludes other glass vessels. Meaning "a glass mirror" is from 14c. Meaning "glass filled with running sand to measure time" is from 1550s; meaning "observing instrument" is from 1610s.
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy).
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Definitions of glassy from WordNet
resembling glass in smoothness and shininess and slickness; "the pavement was...glassy with water"- Willa Cather;
the glassy surface of the lake
(used of eyes) lacking liveliness;
a glassy stare
(of ceramics) having the surface made shiny and nonporous by fusing a vitreous solution to it;