Worker meriting a kinder classification? (6)

I believe the answer is:

sorter

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

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

I don't understand the rest of the clue.

Can you help me to learn more?

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