Countries seen in April and September (5)
I believe the answer is:
lands
'countries' is the definition.
('land' can be a synonym of 'country')
'in april and september' is the wordplay.
'in' indicates the answer is hidden within the clue.
'LANDS' is hidden within 'april and september'.
'seen' is the link.
(Other definitions for lands that I've seen before include "See 21" , "Obtains" , "Comes ashore" , "Alights" .)