Very funny hour I sail at sea (9)
I believe the answer is:
hilarious
'very funny' is the definition.
(I've seen this before)
'hour i sail at sea' is the wordplay.
'at sea' is an anagram indicator.
'hour'+'i'+'sail'='hourisail'
'hourisail' anagrammed gives 'HILARIOUS'.
(Other definitions for hilarious that I've seen before include "Uriah's oil (anag.)" , "Extremely amusing" , "Louis' hair! (anag)" , "Priceless!" , "A scream" .)