The most common and most likely answer to this crossword clue is the 10 letter word WAIT-A-BIT
I've seen this crossword clue in The Guardian
W
A
I
T
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A
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B
I
T
Buddy explains!
The straight part
We know that "Hang on/a thorny plant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case hang on/a thorny plant = wait-a-bit.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 WAIT-A-BIT mean?
WAIT-A-BIT noun- Any of certain plants with sharp hooked thorns found in southern and eastern Africa.
- Certain thorny shrubs and trees of North America