Slacker lied about beginning résumé (5)
I believe the answer is:
idler
'slacker' is the definition.
(I've seen this in another clue)
'lied about beginning resume' is the wordplay.
'about' indicates an anagram.
'beginning' says to take the initial letters.
The first letter of 'resume' is 'r'.
'lied' with letters rearranged gives 'idle'.
'idle'+'r'='IDLER'
(Other definitions for idler that I've seen before include "Riled (anag)" , "Man off watch" , "Not working so hard" , "Bum" , "Laggard" .)