Blot out absence of effort over beginning of resits (5)
I believe the answer is:
erase
'blot out' is the definition.
(thesaurus)
'absence of effort over beginning of resits' is the wordplay.
'absence of effort' becomes 'ease' (I've seen this before).
'over' means one lot of letters goes inside another.
'beginning of' says to take the initial letters.
The first letter of 'resits' is 'r'.
'ease' going around 'r' is 'ERASE'.
(Other definitions for erase that I've seen before include "Destroy recording on audio or video tape" , "Remove evidence of" , "Eliminate" , "Efface" , "Remove, wipe out" .)