gnječiti

1. to mash; to squash; to crush
   Gnječim kuvani krompir viljuškom za pire. — I'm mashing boiled potatoes with a fork for the purée.
   Nemoj da gnječiš paradajz u kesi! — Don't squash the tomatoes in the bag!
2. colloq. (gnječiti se) to be squashed in a crowd; to be crammed
   Svako jutro se gnječimo u punom autobusu. — Every morning we get squashed on a packed bus.

The perfective is zgnječiti.