Noble women tot up letters (10)

I believe the answer is:

countesses

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

'noble women' is the definition.
The definition and answer can be both people as well as being plural nouns.
Perhaps you can see a link between them that I can't see?

'tot up letters' is the wordplay.
'tot up' becomes 'count' (I can't justify this - if you can you should give a lot more credence to this answer).
'letters' becomes 'esses' (more than one S).
'count'+'esses'='COUNTESSES'

Can you help me to learn more?

I've seen this clue in The Guardian.

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