“Plane” is noun; “plain” is adjective.

What about ‘plain’ as a flatland?

(I’m reaching the point where I’ve been staring at a word too long and it starts to look wrong no matter what I try.)

Wikipedia says “plain”:

http://en.wikipedia.org/wiki/Flood_plain

So does Webster’s

It is most definitely not plane.

But http://www.answers.com/topic/flood-plane says flood plane…

and http://www.usingenglish.com/forum/ask-teacher/8578-flood-plain-flood-plane.html says both…

The United States Geological Survey consistently uses “flood plain”.

I am wrong. Sorry. Cross-eyed also. It is flood plain.

Think of the Great Plains.

WRONG?!
Gail, i’m going to have to become a true atheist now!!

**Begins to take down her shrine…**

@Del. You supplied the hagiography. I am simply the hag.

Definitely “flood plain.” My husband owns an insurance agency and the term is used all the time. Refers to a low flat area where there might be flooding, hence a “plain.” Although, plane as in a surface would work semantically, it’s not the correct term.

@ gail – I am surprised at you too!

Hahaha, the pun made up for it all. The shrine goes back up tomorrow.

I’m a born again Gailcalledian! My faith is restored!

Yeah Flood Plain would be land that could flood. A flood Plane wouldn’t be one I’d want to get on… ;-) I’d need two Valiums to even consider it. Heck, I need them now cause you got me thinking about it!

It’s Plain.

Yes, it’s plainly clear that it’s plain.

Yeah I learned it in science.

It should be plane, as used in geometry. The water level forms a plane, a flat surface level in all directions. Even though the people from FEMA refer to a Flood Plain, they are using it incorrectly. I don’t know why. The term refers to the level of the water not to the topography underneath. I have been underwriting insurance, including flood for over thirty years and your husband is wrong.

I’ve been trying to figure why everyone calls it a floodplain because like InsuranceGuy says, a plane of water would literally describe a floodplain. But all the dictionaries and other sources are saying Floodplain. A flood is not plain, however as one said, there are “The Great Plains”, which are truly plains.

So now I’m truly confused… someone find a straight jacket please!

@Micanou I think you mean strait jacket :)

Well, a plane is a flat geometric shape and a plain is a flat geological shape so I think either is potentially correct, but floodplain is what is generally used, meaning a flat geological surface that is prone to flooding.

the OED states:
plain, noun: a large area of flat land with few trees

flood plain: an area of of low lying land adjacent to a river that is subject to flooding

Consider plane geometry.