Fellow residents make dull friends (9)

I believe the answer is:

flatmates

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'fellow residents' is the definition.
The definition and answer can be both people as well as being plural nouns.
Perhaps they are linked in a way I don't understand?

'dull friends' is the wordplay.
'dull' becomes 'flat' (synonyms).
'friends' becomes 'mates' (mate is a kind of friend).
'flat'+'mates'='FLATMATES'

'make' is the link.

Can you help me to learn more?

(Another definition for flatmates that I've seen is " Home sharers".)

I've seen this clue in The Mirror.

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