Turn of century suits put on for graduation (5)
I believe the answer is:
notch
'graduation' is the definition.
(notches might divide or grade things)
'turn of century suits put on' is the wordplay.
'turn of' says the letters should be written backwards (I've seen 'turn' mean this).
'century' becomes 'ton' (both can mean one hundred of something).
'suits' becomes 'CH' (abbreviations for clubs and hearts).
'put on' says to put letters next to each other (some letters go on or after others).
'ton' written backwards gives 'not'.
'not'+'ch'='NOTCH'
'for' is the link.
(Other definitions for notch that I've seen before include "Nick; small cut" , "Snick" , "Nick made in something as a record" , "Secure" , "V-shaped incision" .)