The most common and most likely answer to this crossword clue is the 8 letter word FLATLAND
I've seen this crossword clue in The Daily Telegraph
F
L
A
T
L
A
N
D
Buddy explains!
The straight part
We know that "Plain area" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case plain area = flatland.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FLATLAND mean?
FLATLAND noun- A land area free of woodland, cities, and towns; open country.
- A wide, open space that is usually used to grow crops or to hold farm animals.
- A place where competitive matches are carried out.
- Any of various figurative meanings, regularly dead metaphors.
- An urban region with many flats or apartments to rent.
- A lamentation.
- An expanse of land with relatively low relief, usually exclusive of forests, deserts, and wastelands.
- A level or flat surface.
- A flat surface extending infinitely in all directions (e.g. horizontal or vertical plane).
- A level of existence or development. (eg, astral plane)
- A roughly flat, thin, often moveable structure used to create lateral force by the flow of air or water over its surface, found on aircraft, submarines, etc.
- (Unicode) Any of a number of designated ranges of sequential code points.
- An imaginary plane which divides the body into two portions.
- A tool for smoothing wood by removing thin layers from the surface.
- An airplane; an aeroplane.
- Any of various nymphalid butterflies, of various genera, having a slow gliding flight. Also called aeroplanes.
- The butterfly Bindahara phocides, family Lycaenidae, of Asia and Australasia.
- A deciduous tree of the genus Platanus.
- (Northern UK) A sycamore.