The most common and most likely answer to this crossword clue is the 10 letter word INACCURACY
I've seen this crossword clue in The Daily Telegraph
I
N
A
C
C
U
R
A
C
Y
Buddy explains!

The straight part
We know that "slip" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case slip = inaccuracy.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 INACCURACY mean?
INACCURACY noun- The property of being inaccurate; lack of accuracy.
- A statement, passage etc. that is inaccurate or false.
- Incorrect calibration of a measuring device, or incorrect use; lack of precision.