In sea was Hesperus flooded? (5)
I believe the answer is:
awash
'flooded?' is the definition.
('awash' can be a synonym of 'flooded')
'in sea was hesperus' is the wordplay.
'in' indicates a hidden word.
'AWASH' is hidden within 'sea was hesperus'.
(Other definitions for awash that I've seen before include "Crawling" , "Level with the water surface" , "Flood" , "Letting in the sea" , "Swimming" .)