Also known as a sail somehow (5)
I believe the answer is:
alias
'also known as' is the definition.
('alias' can be a synonym of 'also known as')
'a sail somehow' is the wordplay.
'somehow' indicates an anagram.
'sail' is an anagram of 'lias'.
'a'+'lias'='ALIAS'
(Other definitions for alias that I've seen before include "Alternative identity" , "one's assumed" , "Handle that isn't genuine" , "Otherwise called" , "aka" .)