They don't play principal parts (6)

I believe the answer is:

agents

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

'parts' is the definition.
The answer and definition can be both natural objects as well as being plural nouns.
Maybe you can see a link between them that I don't see?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for agents that I've seen before include "They act for others" , "Spies" , "They operate on behalf of others" , "Factors" , "Sales reps" .)

I've seen this clue in The Globe and Mail and The Irish News.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.