penny-in-the-slot
/ˌpɛni ɪn ðə ˈslɒt/British
adjective
Designating or relating to a machine or mechanical device (as a weighing machine, dispensing machine, etc.) actuated by the fall of a penny inserted through a slot or narrow opening.
noun
A penny-in-the-slot machine. rare.
Origin
Late 19th century; earliest use found in The Boston Globe. From penny + in + the + slot.