In favour of returning at mid-April (3)
I believe the answer is:
for
'in favour' is the definition.
(I've seen this before)
'of returning at mid-april' is the wordplay.
'returning' shows that the letters should be reversed in order.
'at' says to put letters next to each other.
'mid' says to take the centre.
The middle letter of 'april' is 'r'.
'of' reversed gives 'fo'.
'fo'+'r'='FOR'
(Other definitions for for that I've seen before include "Approving" , "Pro" , "See 24" , "Favouring" , "and 16 and 20: Notwithstanding" .)