Dominant wolf, if threatening packs (5)
I believe the answer is:
fifth
'dominant' is the definition.
(the fifth note of a musical scale is the dominant)
'wolf if threatening packs' is the wordplay.
'packs' says the answer is hidden in the clue (I've seen 'packing' mean this).
'FIFTH' is hidden within 'wolf if threatening'.
(Other definitions for fifth that I've seen before include "20 per cent" , "Twenty percent" , "Fraction" , "Interval of three tones and a semitone" , "- Column is a group working for the enemy" .)