If an object or a surface gleams, it reflects light because it is shiny and clean.

You can refer to the light reflected from something as a gleam .

If a light or the sun or moon gleams, it shines faintly.

A gleam of light is a pale, clear light.

If your eyes gleam, they look bright and show that you are excited or happy.

If someone has a gleam in their eye, their eyes show a particular feeling.

A gleam of something is a faint sign of it.

If you say that something is only a gleam in someone's eye at present, you mean that it is only being planned or considered, and has not yet been properly begun.