Chew part with energy (4)
I believe the answer is:
bite
'chew' is the definition.
(thesaurus)
'part with energy' is the wordplay.
'part' becomes 'bit' (both mean a piece of something).
'with' says to put letters next to each other.
'energy' becomes 'e' (physics symbol as in E=mci).
'bit'+'e'='BITE'
(Other definitions for bite that I've seen before include "Snake or insect wound" , "Take bait; sting" , "Get teeth into" , "The taking of bait by a fish" , "Grip with teeth" .)