Either of the lads in prison for arson? (4)
I believe the answer is:
twin
'arson?' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'either of the lads in prison' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'in' is present in the answer.
A single letter 'w' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'for' acts as a link.
Can you help me to learn more?
(Other definitions for twin that I've seen before include "eg Pollux or Remus" , "(Town) paired with another" , "One of a matching pair" , "Very much like" , "indistinguishable from the next?" .)