Crossword Genius

A powerful car tails off? My trip needs something much more powerful (9)

Ross

I believe the answer is:

astronaut

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

'a powerful car' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for astronaut that I've seen before include "Space explorer" , "high flier" , "Armstrong or Sharman, say" , "Buzz Aldrin, e.g." , "Space voyager" .)

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