Dear addresses (4)

I believe the answer is:

sirs

I'm a little stuck... Click here to teach me more about this clue!

'dear addresses' is the definition.
Although both the answer and definition are plural nouns, I can't see how they can define each other.

This is the entire clue.

Can you help me to learn more?

(Other definitions for sirs that I've seen before include "men" , "Knights" , "Gentlemen" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app