Sluggard heading off for fix (4)
I believe the answer is:
nail
'for fix' is the definition.
(I've seen this before)
'sluggard heading off' is the wordplay.
'sluggard' becomes 'snail' (I've seen this in another clue).
'heading off' means to remove the first letter.
'snail' with its initial letter removed is 'NAIL'.
(Other definitions for nail that I've seen before include "Secure" , "Horny part of the digit" , "for the carpenter?" , "SECOND PART OF 17" , "Fix with a metal spike" .)