Energy at the back in a certain direction (7)
I believe the answer is:
eastern
'certain direction' is the definition.
'eastern' can be an answer for 'direction' (I've seen this before). I'm not sure about the 'certain' bit.
'energy at the back' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'at the back' becomes 'astern' (I've seen this before).
'e'+'astern'='EASTERN'
'in a' acts as a link.
Can you help me to learn more?
(Other definitions for eastern that I've seen before include "Of the direction of the rising sun" , "in Beijing, possibly" , "From Japan, say" , "Nearest (anag) - oriental" , "Maybe Chinese" .)