The most common and most likely answer to this crossword clue is the 8 letter word HEADBAND
I've seen this crossword clue in The Times
H
E
A
D
B
A
N
D
More clues leading to the result HEADBAND
Buddy explains!

The straight part
We know that "adornment in hair" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case adornment in hair = headband.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 HEADBAND mean?
HEADBAND noun- A strip of fabric worn around the head.
- A hair-accessory, made of a flexible material and curved like a horseshoe, for holding one's hair back.
- A strip of fabric attached to the top of the spine of a book; used as decoration and reinforcement.
- A thin slip of iron on the tympan of a printing-press.