Gather around mother on donkey (5)
I believe the answer is:
amass
'gather' is the definition.
(amass can mean to collect or gather)
'around mother on donkey' is the wordplay.
'around' says the letters should be written in reverse.
'mother' becomes 'ma' (Ma is another word for mother or mum).
'on' means one lot of letters go next to another.
'donkey' becomes 'ass' (ass is a term for a donkey).
'ma' reversed gives 'am'.
'am'+'ass'='AMASS'
(Other definitions for amass that I've seen before include "Put together" , "Sodium chloride" , "store" , "Collect, hoard" , "Gather together, pile up" .)