When sick, I get fifty quid (3)
I believe the answer is:
ill
'when sick' is the definition.
'ill' can be an answer for 'sick' (similar in meaning). I am not sure about the 'when' bit.
'i get fifty quid' is the wordplay.
'get' says to put letters next to each other.
'fifty quid' becomes 'll' (I can't explain this - if you can you should believe this answer much more).
'i'+'ll'='ILL'
Can you help me to learn more?
(Other definitions for ill that I've seen before include "Sickly" , "In short, the state of Chicago" , "I will (abbrev.) (1'2)" , "Ailing" , "Harm" .)