Tip (over)
'tip over' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for upset that I've seen before include "Distressed; overturn" , "Discomfit" , "Surprising result" , "Disturb the balance or stability of" , "Disordered - unexpected defeat" .)
(Other definitions for upend that I've seen before include "Turn top to bottom" , "change things drastically" , "Tip right over" , "Knock over" , "Make a turnover" .)
(Other definitions for keel that I've seen before include "Support on which ship is built" , "Ship's bottom" , "Beam on the hull of a vessel" , "Low part of ship" , "Cool, or it used to be" .)