Wormwood Scrubs, perhaps — or what it’s familiarly known by? (8)
I believe the answer is:
nickname
'wormwood' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
I don't understand how the rest of the clue works.
(Other definitions for nickname that I've seen before include "tag" , "Familiar form of address" , "Familiar moniker" , "Jocular moniker" , "Fond title" .)