One of the kinder postal workers? (6)

'one of the kinder postal workers?' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'one of the' is the wordplay.
I cannot quite see how this works, but
'of' could be 'o' and 'o' is found in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?