Friday's friend (6)
I believe the answer is:
crusoe
'friday's friend' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for crusoe that I've seen before include "Shipwrecked hero" , "See 11" , "Defoe's hero derived" , "Lonely islander" , "Robinson . . . . . . was a famous fictional castaway" .)