1. To fit in(side of something) very snugly or compactly. Sorry, my car is pretty tiny, so you'll all have to just squash in. I know the bag looks small, but the sleeping bag squashes in without a problem.

2. To force or compel someone or something to fit inside of something by crushing, compressing, or compacting them or it. In this usage, a noun or pronoun can be used between "squash" and "in." I only have one suitcase, so I always have to squash in all my clothes whenever I travel. They tried to squash 40 of us in that dinky little classroom.

3. To crush, crumple, or mash something inward. In this usage, a noun or pronoun can be used between "squash" and "in." The bully came over and squashed in my science fair diorama with his fist. Don't sit on the box like that, or you'll squash it in!