The most common and most likely answer to this crossword clue is the 9 letter word GENERALLY
I've seen this crossword clue in Financial Times
G
E
N
E
R
A
L
L
Y
More clues leading to the result GENERALLY
- Shockingly green friend, on the whole
- Source of personal information has to improve, as a rule
- How the top brass operate as a rule?
- Energy running out restricts everyone, as a rule
- Kelly will go to meeting as a rule
- As a rule, has army commander’s regular ploy
- As a rule, army chief left before end of ceremony
Buddy explains!

The straight part
We know that "as a rule" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case as a rule = generally.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 GENERALLY mean?
GENERALLY adverb- Popularly or widely.
- As a rule; usually.
- Without reference to specific details.
- Collectively; as a whole; without omissions.