Collect a male donkey (5)
I believe the answer is:
amass
'collect' is the definition.
(I know that collect can be written as amass)
'a male donkey' is the wordplay.
'male' becomes 'm' (common abbreviation).
'donkey' becomes 'ass' (ass is a term for a donkey).
'a'+'m'+'ass'='AMASS'
(Other definitions for amass that I've seen before include "store" , "Collect or gather" , "Build up" , "Accumulate, pile up" , "Collect, hoard" .)