Conserving energy, passes on the wacky baccy (7)
I believe the answer is:
reefers
'conserving energy passes' is the definition.
Although both the answer and definition are plural nouns, I don't understand how they can define each other.
'on the wacky baccy' is the wordplay.
I cannot quite understand how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for reefers that I've seen before include "Jackets; joints" , "Double-breasted jackets" , "Nautical jackets" , "Joints (sl.)" , "Cannabis cigarettes" .)