Wild fellow, real trouble (5)
I believe the answer is:
feral
'wild' is the definition.
(similar in meaning)
'fellow real trouble' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'trouble' indicates anagramming the letters.
'real' is an anagram of 'eral'.
'f'+'eral'='FERAL'
(Other definitions for feral that I've seen before include "Wild, untamed" , "Flare up, being fierce" , "Escaped-into-wild (animal)" , "Like a wild animal" , "Wild and menacing" .)