Small animal? A small insect, not yet adult (4)
I believe the answer is:
pupa
'not yet adult' is the definition.
(I've seen this before)
'small animal? a small insect' is the wordplay.
I cannot really see how this works, but
'animal?' could be 'pup' (pup is a kind of animal) and 'pup' is present in the answer.
'a' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for pupa that I've seen before include "not yet adult" , "Phase of insect life" , "Pre-adult insect or chrysalis" , "appearance of immaturity" , "Stage of an insect's development" .)