The most common and most likely answer to this crossword clue is the 8 letter word FORELOCK
I've seen this crossword clue in Financial Times
F
O
R
E
L
O
C
K
Buddy explains!
The straight part
We know that "hair" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case hair = forelock.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 FORELOCK mean?
FORELOCK noun- The part of a person's hairstyle which covers the forehead.
- The part of a horse's (or similar animal's) mane that lies on its forehead.
- A wedge pushed through a hole at the end of a bolt to hold it in place.
- To fix in place with a forelock (wedge)