The most common and most likely answer to this crossword clue is the 7 letter word NOSTRIL
I've seen this crossword clue in Financial Times
N
O
S
T
R
I
L
More clues leading to the result NOSTRIL
- Boy comes up on track, not taking a breather
- Some flirt so naughtily lifting part of body
- Opening, glasnost, riled section
- Bono’s trilby covers hole in head
- Opening whereby crooked personality avoids PAYE
- Through this shortly I’ll snort horribly
- One of a pair found in Hooters?
- Opening numbers by Turkey and Israel
- Opening provided by random riots in Holland
- Whiffy slit on right?
Buddy explains!

The straight part
We know that "Opening" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case opening = nostril.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 NOSTRIL mean?
NOSTRIL noun- Either of the two orifices located on the nose (or on the beak of a bird); used as a passage for air and other gases to travel the nasal passages.