Rocky area on eastern tip of Finland (4)
I believe the answer is:
reef
'rocky area' is the definition.
(reef can mean a formation of rock)
'on eastern tip of finland' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'eastern' becomes 'e'.
'tip of' suggests taking the first letters.
The initial letter of 'finland' is 'f'.
're'+'e'+'f'='REEF'
(Other definitions for reef that I've seen before include "Kind of knot (avoided by sailors?)" , "Gather up" , "Chain of rocks underwater" , "Submerged ridge near the surface of the sea" , "Rock in shallow water" .)