The most common and most likely answer to this crossword clue is the 5 plus 7 letter word EMILY DAVISON
I've seen this crossword clue in Financial Times
E
M
I
L
Y
D
A
V
I
S
O
N
Buddy explains!
The straight part
We know that "One of 14" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one of 14 = emily davison.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.