Limit on head wear (3)
I believe the answer is:
cap
I believe this is a triple definition!
'limit' is the first definition.
(I know that cap is a more specific form of limit)
'on' is a link.
'head' is the second definition.
(both can mean the top of something)
'wear' is the third definition.
(I know that Cap is a wear)
(Other definitions for cap that I've seen before include "Stopper" , "Soft headgear" , "Covering for head or bottle" , "Seal off oil-well" , "Outdo; brimless hat" .)