Sort of exercise Greek character gets in nick (4-2)
I believe the answer is:
chin-up
'sort of exercise' is the definition.
'greek character gets in nick' is the wordplay.
'greek character' becomes 'nu' (letter from the Greek alphabet).
'gets in' means one lot of letters goes inside another.
'nick' becomes 'chip' (synonyms).
'nu' placed inside 'chip' is 'CHIN-UP'.
(Other definitions for chin-up that I've seen before include "Be of good cheer - elevate mandible" , "Exhortation to stay cheerful in difficult circumstances" , "Keep cheerful! (colloq.)" , "Remain cheerful, elevate mandible" , "Show courage with elevated mandible" .)