Desire endless purges (4)
I believe the answer is:
urge
'desire' is the definition.
(I know that urge is a type of desire)
'endless purges' is the wordplay.
'endless' means to look at the middle letters.
The central letters of 'purges' are 'URGE'.
(Other definitions for urge that I've seen before include "Sudden inclination to do something" , "Strong impulse, desire" , "Plead" , "Propel, drive onward" , "'Spur on, encourage (4)'" .)