Fool picked up then let go of sweet (7)
I believe the answer is:
gumdrop
'sweet' is the definition.
(gumdrop is a kind of sweet)
'fool picked up then let go of' is the wordplay.
'fool' becomes 'mug' (synonyms).
'picked up' is a reversal indicator.
'then' says to put letters next to each other.
'let go of' becomes 'drop'.
'mug' back-to-front is 'gum'.
'gum'+'drop'='GUMDROP'
(Other definitions for gumdrop that I've seen before include "Firm jelly sweet" , "It may be sucked" , "Fungus attacking wood" , "Jelly-like sweet" , "Gelatinous type of sweet" .)