Apathetic face of passenger in fastback (5)

I believe the answer is:

tepid

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'apathetic' is the definition.
(thesaurus)

I cannot understand how the rest of the clue works.

(Other definitions for tepid that I've seen before include "Not very warm (water)" , "Not very enthusiastic" , "Warmish" , "without enthusiasm" , "Moderately warm" .)

I've seen this clue in The Daily Express.

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