Joiner held by policemen temporarily (6)
I believe the answer is:
cement
'joiner' is the definition.
(I've seen this before)
'held by policemen temporarily' is the wordplay.
'held by' indicates a hidden word.
'CEMENT' is hidden in the letters of 'policemen temporarily'.
(Other definitions for cement that I've seen before include "Ingredient in mortar" , "It hardens when mixed with water" , "joiner" , "Binding substance as for bricks" , "material for bonding" .)