The most common and most likely answer to this crossword clue is the 8 letter word BLITHELY
I've seen this crossword clue in Financial Times
B
L
I
T
H
E
L
Y
More clues leading to the result BLITHELY
Buddy explains!

The straight part
We know that "in a casual way" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in a casual way = blithely.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 BLITHELY mean?
BLITHELY adverb- Without care, concern, or consideration.
- In a joyful, carefree manner.
- In a kind manner.