Make the boss lie to the head of police? That’s on! (8)
I believe the answer is:
possible
'on' is the definition.
(thesaurus)
'make the boss lie to the head of police?' is the wordplay.
'make' is an anagram indicator.
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'the head of' suggests taking the first letters.
The initial letter of 'police' is 'p'.
'boss'+'lie'='bosslie'
'bosslie' is an anagram of 'ossible'.
'ossible' put after 'p' is 'POSSIBLE'.
'that's' is the link.
(Other definitions for possible that I've seen before include "Conceivable, practicable" , "Feasible achievable" , "Potential" , "Conceivable, imaginable" , "Capable of being achieved" .)