Scottish girl sails terribly close to shore (6)
I believe the answer is:
lassie
'scottish girl' is the definition.
(I've seen this in another clue)
'sails terribly close to shore' is the wordplay.
'terribly' indicates an anagram.
'close to' says to take the final letters (the close of something is the end).
The final letter of 'shore' is 'e'.
'sails' with letters rearranged gives 'lassi'.
'lassi'+'e'='LASSIE'
(Other definitions for lassie that I've seen before include "dog in pictures" , "Screen canine" , "Movie role for several dog stars" , "Canine film star" , "TV series collie dog" .)