Writer joining a large sort of colony (5)
I believe the answer is:
penal
'sort of colony' is the definition.
(I've seen this in another clue)
'writer joining a large' is the wordplay.
'writer' becomes 'pen' (something which writes).
'joining' is a charade indicator (letters next to each other).
'large' becomes 'L' (eg in clothes sizes).
'pen'+'a'+'l'='PENAL'
(Other definitions for penal that I've seen before include "Involving legal punishment" , "Relating to legal punishment" , "Punishable by law" , "Involving punishment as by the law" , "Punishing" .)