With energy, mention jacket (6)
I believe the answer is:
reefer
'jacket' is the definition.
(thesaurus)
'with energy mention' is the wordplay.
I cannot quite understand how this works, but
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is found within the answer.
The remaining letters 'refer' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for reefer that I've seen before include "Canvas trimmer" , "In slang, a marijuana cigarette" , "Smoking jacket and cigarette" , "Double-breasted jacket for a man" , "Warm jacket - cannabis cigarette" .)