Carriage used in April and August (6)
I believe the answer is:
landau
'carriage' is the definition.
(I've seen this before)
'in april and august' is the wordplay.
'in' indicates the answer is hidden within the clue.
'LANDAU' is hidden within 'april and august'.
'used' acts as a link.
(Other definitions for landau that I've seen before include "An auld type of carriage" , "Old four-wheeled covered carriage" , "Old-fashioned four-wheeled covered carriage" , "Horse-drawn carriage or car with folding top" , "Transport" .)