Crossword Genius

Overload current charging motor (4)

Ross

I believe the answer is:

taxi

I'm a little stuck... Click here to teach me more about this clue!

'motor' is the definition.
(thesaurus)

'overload current charging' is the wordplay.
I cannot quite understand how this works, but
'current' could be 'i' (symbol for electric current) and 'i' is located in the answer.
The remaining letters 'tax' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for taxi that I've seen before include "At airport, guide" , "move on ground before take-off" , "Motor vehicle by rank?" , "(Of a plane) move slowly on the ground" , "people carrier?" .)

I've seen this clue in The Independent.
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