Animal so contained in receptacle (5)
I believe the answer is:
bison
'animal' is the definition.
(I've seen this before)
'so contained in receptacle' is the wordplay.
'contained in' means one lot of letters goes inside another.
'receptacle' becomes 'bin' (I've seen this in another clue).
'so' put within 'bin' is 'BISON'.
(Other definitions for bison that I've seen before include "Buffalo (US)" , "North American buffalo" , "European buffalo" , "Big beast" , "brute" .)