The most common and most likely answer to this crossword clue is the 9 letter word QUOTIDIAN
Q
U
O
T
I
D
I
A
N
More clues leading to the result QUOTIDIAN
Buddy explains!

The straight part
We know that "Common" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case common = quotidian.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 QUOTIDIAN mean?
QUOTIDIAN noun- A fever which recurs every day; quotidian malaria.
- A daily allowance formerly paid to certain members of the clergy.
- (usually with definite article) Commonplace or mundane things regarded as a class.
- Recurring every twenty-four hours or (more generally) daily (of symptoms, etc).
- Happening every day; daily.
- Having the characteristics of something which can be seen, experienced, etc, every day or very commonly; commonplace, ordinary, mundane.