Crossword Genius

Essential part of electricity bill (6)

Ross

I believe the answer is:

charge

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'bill' is the definition.
(synonyms)

I cannot understand how the remainder of the clue works.

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(Other definitions for charge that I've seen before include "rate" , "Offensive - fee" , "Attack - require payment" , "person in custody" , "Lord Cardigan's order to his brigade" .)

I've seen this clue in The Hindu.
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