The most common and most likely answer to this crossword clue is the 4 letter word ZITI
Z
I
T
I
Buddy explains!
The straight part
We know that "past/a" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case past/a = ziti.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 ZITI mean?
ZITI noun- A type of penne pasta in the form of long smooth hollow tubes.