Attempts to use knife on Sunday (5)
I believe the answer is:
stabs
'attempts' is the definition.
(I know this)
'knife on sunday' is the wordplay.
'knife' becomes 'stab' (synonyms).
'on' means one lot of letters go next to another.
'sunday' becomes 's'.
'stab'+'s'='STABS'
'to use' acts as a link.
(Other definitions for stabs that I've seen before include "Thrusts a knife into" , "Pierces" , "Wounds with blow of knife" .)