Definition: to indicate by ticking, or making another mark, that you have completed or dealt with items on a list. [British] (This verb has more than one meaning)
E.g.1. I had a long list of things to do today, but I only managed to tick off half of them.
E.g.2. When you’re looking for a figure that’s wrong, it helps to tick off the ones that you are sure are right.
This phrasal verb can be separated.