Definition of petty custom in US English:

petty custom

noun

Scottish
historical
  • A lesser toll or duty; specifically that formerly charged upon goods entering a town or burgh for sale at its markets. Frequently in plural See also "petit custom".

Origin

Late Middle English. From petty + custom [adjective], after post-classical Latin parva custuma.

Pronunciation

petty custom

/ˌpɛti ˈkʌstəm/