If something is as plain as day or as plain as the nose on your face, it is very easy to see, or obvious and easy to understand. He was lying there plain as day, in his hospital gown. It's plain as the nose on your face that this company is wildly undervalued. Note: In old-fashioned British English, you can also say that something is plain as a pikestaff. I saw your grandmother this morning, here as plain as a pikestaff, at the foot of my bed. Note: This expression was originally `plain as a packstaff'. A packstaff was a long stick that pedlars used to carry their bundles. The word `pikestaff' was substituted at a later time: a pikestaff was a long walking stick. Both packstaffs and pikestaffs were very plain and simple.