The most common and most likely answer to this crossword clue is the 8 letter word ORDINARY
I've seen this crossword clue in Financial Times
O
R
D
I
N
A
R
Y
More clues leading to the result ORDINARY
- Plain gold coin used in Kuwait and Yemeni capital
- A dry iron — sadly commonplace
- Regular case from October and November in journal
- Familiar old money invested in track
- Commonplace, a penny-farthing years ago
- Plain gold currency’s unknown
- Currency unknown following gold standard
- Ring road, one not for pedestrian
- Conservative losing head about European currency? That’s normal
- Golden record entered by new bishop
Buddy explains!

The straight part
We know that "Plain" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case plain = ordinary.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 ORDINARY mean?
ORDINARY noun- A person with authority; authority, ordinance.
- Something ordinary or regular.
- (of a judge) Having regular jurisdiction; now only used in certain phrases.
- Being part of the natural order of things; normal, customary, routine.
- Having no special characteristics or function; everyday, common, mundane; often deprecatory.
- Bad or undesirable.