Glassy means smooth and shining like glass, or blank in expression. A glassy sea, glassy eyes, a glassy stare.
Of water it means perfectly flat and reflective, which surfers use as high praise. Of eyes it means unfocused, and it is a sign of illness, exhaustion or drink — a glassy stare is looking without seeing. In geology, a glassy rock cooled too fast for crystals to form. Note glass; and that the word is Middle English.
1adjectiveglassySmooth and shining like glass.
“In the early morning, the lake was glassy and still.”
2adjectiveblankBlank and unfocused, of eyes.
“After drinking all night, he stared at us with glassy eyes.”
glassy is a quality of smoothness or blankness.
Middle English glasy is glass plus -y. Glass comes from Old English glaes and is Germanic.
Middle English
glasy
English, today
glassy
From Middle English glasy, equivalent to glass + y. Compare stq glääsich (“glassy”), Dutch glazig (“glassy”), German Low German glasig (“glassy”), German glasig (“glassy”).
Etymology from Wiktionary, CC BY-SA