The most common and most likely answer to this crossword clue is the 8 letter word CLASSIFY
I've seen this crossword clue in The Times
C
L
A
S
S
I
F
Y
More clues leading to the result CLASSIFY
- Swish clothing provided in catalogue?
- Sort out stylish clothing provided
- Rank girl provided in case of custody
- Stylish clothing one female’s to organise
- Pigeonhole providing stylish envelopes
- Catalogue providing stylish clothes
- Grasping female I rejected, up-market sort
- Grade Form 1 extremely firmly
- Grade in form if last in history
- Order pair of smalls provided in medium
Buddy explains!

The straight part
We know that "Pigeonhole" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pigeonhole = classify.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 CLASSIFY mean?
CLASSIFY verb- To identify by or divide into classes; to categorize
- To declare something a secret, especially a government secret