Nothing on course to relieve irritation (7)
I believe the answer is:
scratch
I believe this clue is a double definition.
'nothing' is the first definition.
(as in making something 'from scratch')
'course to relieve irritation' is the second definition.
(means of relieving a scratch)
'on' is the link.
(Other definitions for scratch that I've seen before include "withdraw from tournament" , "Withdraw from (competition)" , "Insignificant injury" , "Rough and ready" , "not much of a handicap" .)