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

The straight part
We know that "thicket" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case thicket = chaparral.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 CHAPARRAL mean?
CHAPARRAL noun- A region of shrubs, typically dry in the summer and rainy in the winter. The coast of the Mediterranean is such a region.
- The foliage of creosote bush, Larrea divaricata, when used as a medicinal herb.