The most common and most likely answer to this crossword clue is the 9 letter word YESTERDAY
I've seen this crossword clue in The Times
Y
E
S
T
E
R
D
A
Y
More clues leading to the result YESTERDAY
- Cry of joy about desert transformed very recently
- One that lighted fools when the rest weren't born?
- I agree twice to cross the road, horse having gone past
- Leaders of young elephants foolishly strayed very recently
- Cultivation of rye, steady in the past
- Old song that makes me happy about windy desert
- Okay, ate dry crackers about 24 hours ago
- . Starry-eyed Romeo leaving in distress not long ago
- Beatles song certainly rated uncommonly higher than unknown quantity
- Agreement on trade foundering one year previously
Buddy explains!

The straight part
We know that "past" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case past = yesterday.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 YESTERDAY mean?
YESTERDAY noun- The day immediately before today; one day ago.
- The recent past, often disparaging.
- On the day before today.
- As soon as possible.