plain as day

(as) plain as day

Very obvious or noticeable. It's plain as day that they like each other— they've been flirting all evening! In the end, the solution was as plain as day.
See also: plain

*plain as day

 and *plain as a pikestaff 
1. Cliché very plain and simple. (*Also: as ~.) Although his face was as plain as day, his smile made him look interesting and friendly. Fred: I have a suspicion that Marcia is upset with me. Alan: A suspicion? Come on, Fred, that's been plain as a pikestaff for quite some time! 2. and *plain as the nose On one's face Cliché clear and understandable. (*Also: as ~.) The lecture was as plain as day. No one had to ask questions. Jane: I don't understand why Professor Potter has been so friendly this week. Alan: It's plain as the nose on your face. He wants to be nominated for Professor of the Year.
See also: plain

plain as day

Also, plain as the nose on your face. Very obvious, quite clear, as in It's plain as day that they must sell their house before they can buy another, or It's plain as the nose on your face that she's lying. These similes have largely replaced the earlier plain as a packstaff or pikestaff, from the mid-1500s, alluding to the stick on which a peddler carried his wares over his shoulder. The first term, from the late 1800s, is probably a shortening of plain as the sun at midday; the variant dates from the late 1600s.
See also: plain

plain as day

or

plain as the nose on your face

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.
See also: plain

plain as day (or the nose on your face)

very obvious. informal
See also: plain