Looking round for a letter? (8)

I believe the answer is:

circular

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This clue could be a double definition.

'looking round' is the first definition.
'circular' can be an answer for 'round' (I've seen this before). I'm not certain of the 'looking' bit.

'for a letter?' is the second definition.
(type of advertisement)

Can you help me to learn more?

(Other definitions for circular that I've seen before include "Letter or notice copied to a number of people" , "Round; general letter" , "Widely-distributed notice" , "Spherical" , "Perfectly round" .)

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