Mothers spotted cycling together (2,5)
I believe the answer is:
en masse
'together' is the definition.
(French phrase meaning all together)
'mothers spotted cycling' is the wordplay.
I cannot really understand how this works, but
'mothers' could be 'mas' (ma is a kind of mother) and 'mas' is found within the answer.
The remaining letters 'ense' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for en masse that I've seen before include "in concert" , "Sees man (anag.)" , "as a bunch" , "All together - in France (2.5)" , "As a body (Fr.)" .)