The most common and most likely answer to this crossword clue is the 8 letter word HEEDLESS
I've seen this crossword clue in Independent
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More clues leading to the result HEEDLESS
- Lacking caution, he’s seen round parts of Leeds
- Female scoundrel, say, embracing Duke without much thought
- Rash is undesired with head becoming hot
- Rash ambassador meeting journalist not so often
- Paying no attention like the proverbial chicken — using Ecstasy not the answer
- Without regard she’d see line blurred
- The man’s taken round Leeds, unfortunately paying no attention
- That man’s without journalistic direction, lacking in attention
- Hospital eradicating first sign of unwanted rash
- Uncaring ambassador put on eastern robe after changing sides
Buddy explains!

The straight part
We know that "without much thought" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case without much thought = heedless.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 HEEDLESS mean?
HEEDLESS adjective- Unaware, without noticing; inattentive; careless.