Explorer Sebastian (5)
I believe the answer is:
cabot
'explorer sebastian' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cabot that I've seen before include "John (Giovanni) -, navigator, explored N. America" , "Italian explorer (father or son)" , "Name of two Italian navigator-explorers of the New World, father John and son Sebastian" , "One of two explorers" , "famous explorer" .)