Two potentially confusing phrases:
‘Un train’ is a train but ‘en train de…’ means ‘in the process of’.
‘Une théorie’ is ‘a theory’ but also ‘a procession’.
Taken from Collins-Robert dictionary. And also in “False Friends: Faux Amis” Book Two: Ellie Malet Spradbery. Available on amazon.co.uk (www.amazon.co.uk).