Threaten mischievous child on tip (6)
I believe the answer is:
impend
'threaten' is the definition.
(thesaurus)
'mischievous child on tip' is the wordplay.
'mischievous child' becomes 'imp' (I've seen this before).
'on' means one lot of letters go next to another.
'tip' becomes 'end'.
'imp'+'end'='IMPEND'
(Other definitions for impend that I've seen before include "Be imminent or about to happen" , "Become imminent" , "appearing to be imminent" , "seen to be around the corner" , "Threaten; approach" .)