Flier's feet all at sea (7)
I believe the answer is:
leaflet
'flier's' is the definition.
(thesaurus)
'feet all at sea' is the wordplay.
'at sea' indicates an anagram.
'feet'+'all'='feetall'
'feetall' anagrammed gives 'LEAFLET'.
(Other definitions for leaflet that I've seen before include "It may advertise" , "very little greenery" , "Small information sheet" , "Distribute information" , "Circular - flat eel (anag)" .)