The most common and most likely answer to this crossword clue is the 12 letter word MOTORCYCLIST
I've seen this crossword clue in Financial Times
M
O
T
O
R
C
Y
C
L
I
S
T
Buddy explains!

The straight part
We know that "one of the 19?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one of the 19? = motorcyclist.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 MOTORCYCLIST mean?
MOTORCYCLIST noun- Someone who rides a motorcycle