The most common and most likely answer to this crossword clue is the 12 letter word CONSIDERABLE
I've seen this crossword clue in Financial Times
C
O
N
S
I
D
E
R
A
B
L
E
More clues leading to the result CONSIDERABLE
- Significant political party face Republican expert
- . Unusually bad scoreline is of some importance
- Noted judge left in Lincoln
- Believe fit to be great
- Great mind – intelligent
- Major’s Tory party mob half- hearted
- Regard as skilful and substantial
- Think expert worthy of respect
- Regard Labour leader in Lincoln as worthy of respect
- Great message about drone is broadcast
Buddy explains!

The straight part
We know that "Major" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case major = considerable.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 CONSIDERABLE mean?
CONSIDERABLE noun- A thing to be considered, consideration.
- Significant; worth considering.
- Large in amount.