Fall (over) (4)
(Other definitions for keel that I've seen before include "Vessel stabiliser" , "Cool, or it used to be" , "Low part of ship" , "Long base of a ship" , "Long timber" .)
'fall over' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tip that I've seen before include "present!" , "Useful suggestion" , "Hint or dumping ground" , "End - pourboire" , "Useful hint; end" .)