The most common and most likely answer to this crossword clue is the 7 letter word THICKET
T
H
I
C
K
E
T
More clues leading to the result THICKET
- Pass round back of biggish group of trees
- Covert offensive interrupted by yokel
- Offensive yokel in coarse growth
- Voucher admitting Henry Wood
- Growth of vegetation is just what you want outside hospital
- Note around country type source of tremendously dense shrubs
- Dull film with cute alien in coppice
- Hospital authority for travel covers area that’s grown impenetrable
- Brake hard, going into something motorist tries to avoid
- Bulky alien found in copse
Buddy explains!

The straight part
We know that "area that’s grown impenetrable" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case area that’s grown impenetrable = thicket.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 THICKET mean?
THICKET noun- A dense, but generally small, growth of shrubs, bushes or small trees; a copse.
- A dense aggregation of other things, concrete or abstract.
- The collection of many small linked files created when a document is saved in HTML format by some word processors and web site creation software.