The most common and most likely answer to this crossword clue is the 8 letter word SLANTING
I've seen this crossword clue in The Times
S
L
A
N
T
I
N
G
Buddy explains!

The straight part
We know that "at an angle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case at an angle = slanting.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 SLANTING mean?
SLANTING verb- To lean, tilt or incline.
- To bias or skew.
- To lie or exaggerate.
- The state or quality of being slanted.
- Out of the perpendicular, not perpendicular.