Male in the morning penning antelope in oversize container (6)
I believe the answer is:
magnum
'oversize container' is the definition.
(large wine bottle)
'male in the morning penning antelope' is the wordplay.
'male' becomes 'm' (common abbreviation).
'in the morning' becomes 'am' (AM on a clock).
'penning' indicates putting letters inside.
'antelope' becomes 'gnu' (gnu is a kind of antelope).
'am' enclosing 'gnu' is 'agnum'.
'm'+'agnum'='MAGNUM'
'in' is the link.
(Other definitions for magnum that I've seen before include "Twice the normal-size wine bottle" , "Size of wine bottle; gun" , "1.5 litre wine bottle" , "Two champers bottles in one" , "1 1/2 litre champagne bottle" .)