Is it to be sniffed at? (5)
I believe the answer is:
smell
'at?' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for smell that I've seen before include "Sniff" , "stink" , "Scent" , "Aroma" , "Unpleasant odour" .)