Points out, as an informer (5)

I believe the answer is:

snout

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'an informer' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'points out' is the wordplay.
'points' becomes 'sn'.
'sn'+'out'='SNOUT'

'as' acts as a link.

Can you help me to learn more?

(Other definitions for snout that I've seen before include "Tobacco -- hooter" , "Nose and mouth of a mammal" , "Projecting nasal area of animal" , "Pig's nose" , "Schnozzle" .)

I've seen this clue in the Evening Standard.

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