The most common and most likely answer to this crossword clue is the 9 letter word HOUSEHOLD
I've seen this crossword clue in Financial Times
H
O
U
S
E
H
O
L
D
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 = household.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 HOUSEHOLD mean?
HOUSEHOLD noun- Collectively, all the persons who live in a given house; a family including attendants, servants etc.; a domestic or family establishment.
- A line of ancestry; a race or house.
- Belonging to the same house and family.
- Found in or having its origin in a home.
- Widely known to the public; familiar.