The most common and most likely answer to this crossword clue is the 9 letter word MINIMISED
I've seen this crossword clue in The Daily Telegraph
M
I
N
I
M
I
S
E
D
Buddy explains!

The straight part
We know that "Made light of" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case made light of = minimised.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 MINIMISED mean?
MINIMISED verb- To make (something) as small or as insignificant as possible.
- To remove (a window) from the main display area, collapsing it to an icon or caption.
- To treat (someone) slightingly.