Synonyms for Squish:

n.

grind, rub, press, scrunch, nip, depress. squish (noun)
slop, slosh, splash, splosh, squelch.

v.

flatten (verb)
compress, deflate, even, level, flatten, plane, smooth, grade.
motion (verb)
slop, slosh, splash, splosh, squelch.
squash (verb)
scrunch, press, flatten.

Other synonyms:

Other relevant words:
grind, press, scrunch, splash, slop, splosh, squelch, slosh.