It measures current in the morning and energy used in new term (7)
I believe the answer is:
ammeter
'it measures current' is the definition.
(I've seen this before)
'morning and energy used in new term' is the wordplay.
'morning' becomes 'am'.
'and' is a charade indicator (letters next to each other).
'energy' becomes 'e' (physics symbol as in E=mc2).
'used in' is an insertion indicator.
'new' is an anagram indicator.
'term' with letters rearranged gives 'metr'.
'e' put within 'metr' is 'meter'.
'am'+'meter'='AMMETER'
'in the' acts as a link.
(Other definitions for ammeter that I've seen before include "Instrument measuring electrical current" , "Instrument that measures electric current." , "Current-measurer" , "Device that measures the flow of electrical current" , "Device measuring electric current" .)