By the way (12)
'by the way' is the definition.
(synonyms)
This is all the clue.
(Another definition for incidentally that I've seen is " By the way - deny it in call (anag)".)
'by the way' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for in passing that I've seen before include "Where footballer may show skill" , "casually" , "by the way" .)