Let loose, rhino initially seen in charge (4)
I believe the answer is:
free
'let loose' is the definition.
(I've seen this before)
'rhino initially seen in charge' is the wordplay.
'initially' says to take the initial letters.
'seen in' indicates putting letters inside.
'charge' becomes 'fee' (fee is a kind of charge).
The initial letter of 'rhino' is 'r'.
'r' placed inside 'fee' is 'FREE'.
(Other definitions for free that I've seen before include "unemployed" , "Unrestricted" , "Unencumbered" , "Lavish" , "Generous, rid, available" .)