German car: ordinary, sound (5)
I believe the answer is:
audio
'sound' is the definition.
(audio means sound)
'german car ordinary' is the wordplay.
'german car' becomes 'audi' (I've seen this in another clue).
'ordinary' becomes 'O' (abbreviation e.g. O-Levels).
'audi'+'o'='AUDIO'
(Other definitions for audio that I've seen before include "Prefix signifying sound or hearing" , "Reproduced sound" , "Electronic sound reproduction" , "- - visual aids" , "Sound recording" .)