Black ones were a penny each (6)
I believe the answer is:
stamps
'black ones' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how they can define each other.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for stamps that I've seen before include "Tokens stuck on letters" , "Items of interest to a philatelist" , "Gummed receipts of postal fees" , "creates an impression" , "Imprints" .)