It's useful in drawing things (7)

I believe the answer is:

tractor

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

'things' 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 how the rest of the clue works.

Can you help me to learn more?

(Other definitions for tractor that I've seen before include "Farming vehicle" , "I can draw" , "Vehicle for pulling farm machinery" , "Agricultural machine" , "Vehicle used on farms" .)

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