Body of water airman entered carelessly (13)
I believe the answer is:
mediterranean
'body of water' is the definition.
(Mediterranean is an example)
'airman entered carelessly' is the wordplay.
'carelessly' indicates anagramming the letters.
'airman'+'entered'='airmanentered'
'airmanentered' anagrammed gives 'MEDITERRANEAN'.
(Other definitions for mediterranean that I've seen before include "Inland sea" , "Sea linking three continents" , "Sea south of Europe" , "Sea north of Africa" .)