There are several 'en X' phrases in use in English, all borrowed from French I think (but creating a phrase of this sort is a 'productive mechanism' in circles where people know and use French, so an 'en X' phrase may sometimes be coined in English: I can't think of any at the moment, but I'm sure I've heard native English students of French doing it).
Examples of the commoner sort are 'en route', 'en famille' and (rarer) 'en passant'; there are also the more clearly French borrowings related to cuisine, such as 'en croûte' or 'en daube'.
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