Power for empty crate (5)
I believe the answer is:
force
'power' is the definition.
(I know that power can be written as force)
'for empty crate' is the wordplay.
'empty' suggests removing the centre.
'crate' with its middle removed is 'ce'.
'for'+'ce'='FORCE'
(Other definitions for force that I've seen before include "Physical coercion" , "Strength - compulsion" , "Power; army" , "Powerful effect or influence" , "Strength, power" .)