Trashed Application iMovie

I can't use iMovie because it said the Application is in the Trash but all I can see in the trash is iMovie temporary items - so not the programme itself. So I can't click on the iMovie icon in the dock at the bottom of the screen because it says there's no programme there, it's not in the applications folder and I can't find it in the trash. I can only find previous movies I've made saved in the documents. How can I fix this problem?