The most common and most likely answer to this crossword clue is the 7 letter word LEADING
I've seen this crossword clue in Financial Times
L
E
A
D
I
N
G
More clues leading to the result LEADING
- Advanced up cliff
- First stage of relay with a big noise being introduced
- Principal begging head to leave
- Blank space in print is most important
- Principal appealing to Miss Penny
- In front but poorly aligned
- Principal drug hidden among cargo
- Key support for entertaining a big noise
- Prime suspect in deal with Government
- Ahead, making case – not quietly at first
Buddy explains!

The straight part
We know that "Key" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case key = leading.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 LEADING mean?
LEADING verb- To cover, fill, or affect with lead
- To place leads between the lines of.
- (heading) To guide or conduct.
- To guide or conduct, as by accompanying, going before, showing, influencing, directing with authority, etc.; to have precedence or preeminence; to be first or chief; — used in most of the senses of the transitive verb.
- (heading) To begin, to be ahead.
- To draw or direct by influence, whether good or bad; to prevail on; to induce; to entice; to allure
- To tend or reach in a certain direction, or to a certain place.
- To produce (with to).
- (transitive) To live or experience (a particular way of life).
- Providing guidance or direction.
- Ranking first.
- Occurring in advance; preceding.
- An act by which one is led or guided.
- Vertical space added between lines; line spacing.