A filling sort of paste (5)

I believe the answer is:

putty

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'paste' is the definition.
(thesaurus)

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

(Other definitions for putty that I've seen before include "Glazier's paste" , "Malleable form of glas holder" , "Window-sealing paste" , "Window fixer" , "Whiting and linseed oil paste" .)

I've seen this clue in the Evening Standard.

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