Jolly old saint (4)
'jolly old saint' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nick that I've seen before include "Lift" , "Prison (sl.)" , "Catch" , "Mark" , "go off with > form" .)
(Other definitions for nicholas that I've seen before include "Man's name; last tsar" , "Patron saint of children and Russia" , "Russia's last emperor ..." , "Patron saint of Greece (and Liverpool)" , "Novel featuring Dotheboys Hall" .)