Island nation: endless locks securing it (5)
I believe the answer is:
haiti
'island nation' is the definition.
(country on the island of Hispaniola)
'endless locks securing it' is the wordplay.
'endless' means to remove the last letter.
'locks' becomes 'hair' (I've seen this before).
'securing' means one lot of letters goes inside another.
'hair' with its final letter removed is 'hai'.
'hai' placed around 'it' is 'HAITI'.
(Other definitions for haiti that I've seen before include "West Indies country associated with voodoo" , "Country SE of Cuba" , "Country in W Indies, capital Port-au-Prince" , "earthquake-hit area" , "West Indies republic" .)