At pleasure, a detective left one piece with hesitation (2,7)
I believe the answer is:
ad libitum
'with hesitation' is the definition.
Both the definition and answer are adverbs. Perhaps they are linked in a way I don't understand?
'at pleasure a detective left one piece' is the wordplay.
'at pleasure' becomes 'ad lib' (I've seen this before).
'a detective left' becomes 'i' (I can't explain this - if you can you should believe this answer much more).
'one piece' becomes 'tum' (tum is a kind of piece).
'adlib'+'i'+'tum'='AD LIBITUM'
Can you help me to learn more?
(Another definition for ad libitum that I've seen is " As much and as often as desired".)