Popular legend maintaining Noah is at sea (11)
I believe the answer is:
fashionable
'popular' is the definition.
(similar in meaning)
'legend maintaining noah is at sea' is the wordplay.
'legend' becomes 'fable' (synonyms).
'maintaining' is an insertion indicator.
'at sea' indicates anagramming the letters.
'noah'+'is'='noahis'
'noahis' with letters rearranged gives 'shiona'.
'fable' going around 'shiona' is 'FASHIONABLE'.
(Other definitions for fashionable that I've seen before include "A la mode" , "Trendy" , "Modish" , "What's in" .)