Knowledgeable, popular pro overcoming the sea (8)
I believe the answer is:
informed
'knowledgeable' is the definition.
(similar in meaning)
'popular pro overcoming the sea' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'pro' becomes 'for' (I've seen this in another clue).
'overcoming' says to put letters next to each other (in a down clue, some letters go above others).
'the sea' becomes 'med' (abbreviation of Mediterranean).
'in'+'for'+'med'='INFORMED'
(Other definitions for informed that I've seen before include "Gave knowledge to" , "Imparted knowledge" , "Passed on knowledge" , "Expert" , "Told" .)