Male antelope in reserve eats only occasionally, a challenge for charity (3,6)
I believe the answer is:
ice bucket
'a challenge for charity' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'male antelope in reserve eats only occasionally' is the wordplay.
'male antelope' becomes 'buck' (I've seen this before).
'in' indicates putting letters inside.
'reserve' becomes 'ice ' (both can mean aloofness).
'only occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
The alternating letters of 'eats' are 'et'.
'ice'+'et'='iceet'
'buck' put into 'iceet' is 'ICE BUCKET'.
Can you help me to learn more?
(Other definitions for ice bucket that I've seen before include "To get cooler" , "Holder of frozen water" , "What waiter brings" , "Wine chiller" , "Wine cooler" .)