The most common and most likely answer to this crossword clue is the 10 letter word ACCUSTOMED
I've seen this crossword clue in Financial Times
A
C
C
U
S
T
O
M
E
D
More clues leading to the result ACCUSTOMED
- Brought to face charges, man being brought in is familiar
- Used clever remark when turning in defendant
- Cat kept by defendant very much at home
- Scud came to ground as usual
- Male in charge meets old copper as usual
- Cat kept by defendant as familiar
- Familiar cat sheltered by defendant
- Cat kept by defendant at home
- Used someone in dock to house cat
- Familiar male cat adopted by defendant
Buddy explains!

The straight part
We know that "Familiar" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case familiar = accustomed.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 ACCUSTOMED mean?
ACCUSTOMED adjective- (of a person) Familiar with something through repeated experience; adapted to existing conditions.
- (of a thing, condition, activity, etc.) Familiar through use; usual; customary.
- Frequented by customers.