Portion of small animal (5)
I believe the answer is:
share
'portion' is the definition.
(I know that portion can be written as share)
'small animal' is the wordplay.
I cannot really understand how this works, but
'small' could be 's' (abbreviation - e.g. clothes size) and 's' is present in the answer.
'animal' could be 'hare' (I have seen 'Swift animal ' mean 'hare' so perhaps 'animal' could also mean 'hare') and 'hare' is located in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for share that I've seen before include "Give portion to others" , "Portion, allotment" , "Cutting blade" , "Distribute" , "Part, portion" .)