Ridiculous anger gripping little brother or sister (7)
I believe the answer is:
risible
'ridiculous' is the definition.
(I've seen this before)
'anger gripping little brother or sister' is the wordplay.
I cannot quite understand how this works, but
'little' could be 'l' (abbreviation) and 'l' is found in the answer.
'brother' could be 'sib' (short for sibling) and 'sib' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for risible that I've seen before include "Causing laughter - beyond a joke" , "Laughter-provoking" , "Laughable, amusing" , "Laughable, really ridiculous" , "making one laugh" .)