To plan without taking into account all the necessary or important factors or people. It was originally used to describe one who did not consult one's host, such as an innkeeper, when calculating one's lodging expenses. A: "You made plans for Mother's Day without even asking your mom what she wants to do?" B: "I know, I really reckoned without my host on that one."

A very large number or collection of people or things. We had a whole host of problems on opening night, but I think most of the issues have been resolved. While the film has been receiving positive reviews from critics, there's a host of fans who are upset with the way it turned out.