Sort of glass promenade (4)

I believe the answer is:

pier

I'm a little stuck... Click here to teach me more about this clue!

'sort of glass' is the definition.
(pier glass is a type of glass)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for pier that I've seen before include "Platform out to sea" , "Promenade over water" , "Upright member" , "Building projecting into the sea" , "A jetty or promenade" .)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app