All right to hold in animal sound (4)
I believe the answer is:
oink
'animal sound' is the definition.
(I've seen this before)
'all right to hold in' is the wordplay.
'all right' becomes 'ok' ('ok' can be a synonym of 'all right').
'to hold' means one lot of letters goes inside another.
'ok' going around 'in' is 'OINK'.
(Other definitions for oink that I've seen before include "Pig's noise" , "Beastly sound" , "farmyard noise" , "Sow's sound" , "Grunting noise" .)