Crossword Genius

Car was effective for one not needing instructor (10)

Ross

I believe the answer is:

autodidact

'for one not needing instructor' is the definition.
(I've seen this before)

'car was effective' is the wordplay.
'car' becomes 'auto' ('auto' can be a synonym of 'car').
'was effective' becomes 'didact'.
'auto'+'didact'='AUTODIDACT'

(Other definitions for autodidact that I've seen before include "Self-taught person" , "Someone self-taught" , "learner without instructor" , "I skipped school" , "person who taught himself" .)

I've seen this clue in The Guardian.
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