The most common and most likely answer to this crossword clue is the 6 letter word MILDLY
I've seen this crossword clue in Independent
M
I
L
D
L
Y
More clues leading to the result MILDLY
Buddy explains!
The straight part
We know that "Slightly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case slightly = mildly.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 MILDLY mean?
MILDLY adverb- In a mild manner.
- To a mild degree; slightly.