The most common and most likely answer to this crossword clue is the 9 letter word GERMANDER
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More clues leading to the result GERMANDER
Buddy explains!

The straight part
We know that "Herb" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case herb = germander.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 GERMANDER mean?
GERMANDER noun- A Mediterranean herb, Teucrium chamaedrys, historically grown for medicinal use but now mostly as an ornamental miniature hedge in herb gardens.
- Any plant of the genus Teucrium, some with small, pink, white, or pale purple flowers and a small upper lip.