glassy
Smooth and shiny like glass on the surface.
When something is glassy, it looks or feels smooth and shiny like glass. A perfectly calm lake on a windless morning has a glassy surface that reflects the sky like a mirror. Fresh ice on a skating rink looks glassy and slick.
The word often describes surfaces that are smooth enough to see your reflection in them: glassy water, a glassy finish on polished wood, or the glassy shine of a brand-new car after it's been waxed. Glassy things typically have no ripples, bumps, or texture, just like a windowpane.
When describing eyes, glassy takes on a different meaning. Someone with glassy eyes has a blank, unfocused stare. Their eyes might look shiny but vacant, like they're looking past you instead of at you. You might notice this when someone is exhausted, sick with a fever, or lost in thought. Their eyes can resemble glass: smooth and reflective on the surface, but without the spark of attention or awareness behind them.