System of weights in King Priams city (4)
I believe the answer is:
troy
'system of weights' is the definition.
(troy is a kind of system of weights)
'king priams city' is the wordplay.
I cannot really see how this works, but
'king' could be 'r' (abbreviation for rex, king in Latin) and 'r' is located in the answer.
The remaining letters 'toy' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Other definitions for troy that I've seen before include "City impacted by long-term investment" , "City of Paris" , "Priam's city" , "Ancient city where fair Helen was a captive" , "Ancient beseiged city" .)