Absence of any chop on the water, making it smooth like glass. Swell creating breaking waves may still be present, glassy doesn't imply complete flatness
used of eyes lacking liveliness; "empty eyes"; "a glassy stare"; "his eyes were glazed over with boredom" (of ceramics) having the surface made shiny and nonporous by fusing a vitreous solution to it; "glazed pottery"; "glassy porcelain"; "hard vitreous china used for plumbing fixtures" resembling glass in smoothness and shininess and slickness; "the glassy surface of the lake"; "the pavement was
Absence of any chop on the water, making it smooth like glass. Swell creating breaking waves may still be present (hopefully), glassy refers just to the absence of surface chop, not to complete flatness
(of ceramics) having the surface made shiny and nonporous by fusing a vitreous solution to it; "glazed pottery"; "glassy porcelain"; "hard vitreous china used for plumbing fixtures"
Resembling glass in its properties, as in smoothness, brittleness, or transparency; as, a glassy stream; a glassy surface; the glassy deep
resembling glass in smoothness and shininess and slickness; "the glassy surface of the lake"; "the pavement was glassy with water"- Willa Cather