It's synonymous, primarily, with "to crush" (6)
I believe the answer is:
squash
'crush' is the definition.
('squash' can be a synonym of 'crush')
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for squash that I've seen before include "juice that's been watered down" , "Press the veg flat on court" , "Soft drink" , "Racket and ball game and a fruit" , "Vegetable on court?" .)