Bar from acting otherwise (5)
I believe the answer is:
ingot
'bar' is the definition.
(thesaurus)
'from acting otherwise' is the wordplay.
'from' says the answer is hidden in the clue.
'INGOT' is hidden in the letters of 'acting otherwise'.
(Other definitions for ingot that I've seen before include "Brick-shaped lump of cast metal" , "Mass of unwrought gold, for instance" , "Mass of precious metal" , "Block (of steel, gold, etc)" , "A lump of metal like gold" .)