For me sea can be formidable (8)
I believe the answer is:
fearsome
'formidable' is the definition.
(I know that formidable can be written as fearsome)
'for me sea can be' is the wordplay.
'can be' indicates an anagram.
'for'+'me'+'sea'='formesea'
'formesea' with letters rearranged gives 'FEARSOME'.
(Other definitions for fearsome that I've seen before include "Horrendous" , "Terrifying" , "Awful" , "Fame rose and became frightening" , "Of frightening appearance" .)