The most common and most likely answer to this crossword clue is the 10 letter word CARELESSLY
I've seen this crossword clue in The Daily Telegraph
C
A
R
E
L
E
S
S
L
Y
More clues leading to the result CARELESSLY
- In slapdash manner around Gravesend without wheels
- Secretive, after spilling cereals without paying attention
- Without a thought, recluse lays ground to ignore what’s proper
- Fondle embracing the French lovely ends with haste
- Yell scares criminal in an offhand way
- Without thinking, start to comment: ‘Are the French sneaky?’
Buddy explains!

The straight part
We know that "with haste" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case with haste = carelessly.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 CARELESSLY mean?
CARELESSLY adverb- Giving the appearance of carelessness; relaxedly.
- Done without care or attention; inattentively.