King flees bad-tempered elk (5)
I believe the answer is:
moose
'elk' is the definition.
(I know that elk can be written as moose)
'king flees bad-tempered' is the wordplay.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'flees' is a deletion indicator.
'bad-tempered' becomes 'morose' (morose means sad or in a bad mood).
'morose' with 'r' taken out is 'MOOSE'.
(Other definitions for moose that I've seen before include "beasts" , "US deer with enormous antlers" , "Large northern deer" , "Animal" , "North American elk" .)