It’s not to be sniffed at! (4)

I believe the answer is:

glue

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

I don't understand the rest of the clue.

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(Other definitions for glue that I've seen before include "Adhesive stuff" , "Paste" , "size" , "Sticky substance" , "Stick together" .)

I've seen this clue in the Evening Standard.

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