Become weaker and pale, with little energy (4)
I believe the answer is:
wane
'become weaker' is the definition.
(I've seen this before)
'pale with little energy' is the wordplay.
'pale' becomes 'wan' ('wan' can be a synonym of 'pale').
'with' means one lot of letters go next to another.
'little' says to take the initial letters.
The initial letter of 'energy' is 'e'.
'wan'+'e'='WANE'
'and' is the link.
(Other definitions for wane that I've seen before include "Decline (in influence)" , "Appearing to decrease in size, the moon say" , "Dwindle" , "Get smaller" , "Grow smaller like the moon" .)