Start sautéing onions until primed for liquid dish (4)
I believe the answer is:
soup
'liquid dish' is the definition.
(I've seen this before)
'start sauteing onions until primed' is the wordplay.
'start' says to take the initial letters.
The initial letters of 'sauteing onions until primed' is 'SOUP'.
'for' is the link.
(Other definitions for soup that I've seen before include "Bisque, for example" , "Eg, potage, broth" , "Stolen plate melted down" , "liquid content in this food" , "First course" .)