The most common and most likely answer to this crossword clue is the 9 letter word IMPETUOUS
I've seen this crossword clue in The Times
I
M
P
E
T
U
O
U
S
More clues leading to the result IMPETUOUS
- Random opium use not ultimately causing rash
- Open University participating in force? Rash
- Sadly time’s up without you heading off — that’s thoughtless
- Headstrong compiler’s sweethearts cradling heads of ugly old uncles
- Reckless drive around centre of Slough
- Rash unionist, one originally taking part in drive
- Rash drive round old university
Buddy explains!
The straight part
We know that "thoughtless" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case thoughtless = impetuous.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 IMPETUOUS mean?
IMPETUOUS adjective- Making arbitrary decisions, especially in an impulsive and forceful manner.
- Characterized by sudden violence or vehemence.