The most common and most likely answer to this crossword clue is the 7 letter word ELAPSED
I've seen this crossword clue in Independent
E
L
A
P
S
E
D
More clues leading to the result ELAPSED
- Went by valley keeping especially to the north
- Section of quaysides Palermo erected are out of date
- Passed in English then went downhill
- Turning white, section editor slipped away
- Pleased criminal passed by
- Expired from return of the French pasty
- Journalist hides mistake that slipped by
- Went by end of terrace, outdated
- Went by ebbing river putting legs in
- Electronic circuits and leads regularly being passed
Buddy explains!

The straight part
We know that "slipped away" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case slipped away = elapsed.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 ELAPSED mean?
ELAPSED verb- (of time) To pass or move by.