Land transformed into sea (7)
I believe the answer is:
estonia
'land' is the definition.
(Estonia is a country)
'transformed into sea' is the wordplay.
'transformed' indicates anagramming the letters.
'into'+'sea'='intosea'
'intosea' is an anagram of 'ESTONIA'.
(Other definitions for estonia that I've seen before include "Republic in northeastern Europe" , "European country, capital Tallinn" , "Northern European country" , "Republic in the Baltic region, once part of USSR" , "'So eat in here in Tallinn, say (7)'" .)