Glass holder (5)

I believe the answer is:

putty

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'glass holder' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

This is all the clue.

Can you help me to learn more?

(Other definitions for putty that I've seen before include "Window-sealing paste" , "Window glass sealant" , "Glazier's paste" , "Whiting and linseed oil paste" , "Window fixer" .)

I've seen this clue in The Globe and Mail.

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