Incidentally, while overtaking... (2,7)

I believe the answer is:

in passing

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'incidentally' is the definition.
(thesaurus)

'while overtaking' is the wordplay.
'while' becomes 'in' (I can't justify this - if you can you should believe this answer much more).
'overtaking' becomes 'passing' ('pass' can be a synonym of 'overtake').
'in'+'passing'='IN PASSING'

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(Other definitions for in passing that I've seen before include "casually" , "Where footballer may show skill" , "by the way" .)

I've seen this clue in The Irish Independent.

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