get, buy, etc. something on tick

get, buy, etc. something on ˈtick

(old-fashioned, British English, informal) get food or other goods and pay for them later: You can only buy things on tick in small shops where they know you well. Tick is probably a short form of ticket and referred to the written note (an IOU) given by a person borrowing something to the lender as proof that they would pay them back or return the goods.
See also: on, something, tick