Say 'Sorry I go so pale at sea' (9)
I believe the answer is:
apologise
'say sorry' is the definition.
(I've seen this before)
'i go so pale at sea' is the wordplay.
'at sea' indicates anagramming the letters.
'i'+'go'+'so'+'pale'='igosopale'
'igosopale' is an anagram of 'APOLOGISE'.
(Other definitions for apologise that I've seen before include "Express regret for a wrong (S, not Z)" , "Recognise fault" , "Express regret (for action)" , "Say sorry, mea culpa" , "Say one is sorry" .)