The most common and most likely answer to this crossword clue is the 7 letter word PACKRAT
P
A
C
K
R
A
T
Buddy explains!
The straight part
We know that "One who compulsively saves" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one who compulsively saves = packrat.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 PACKRAT mean?
PACKRAT noun- Any of several species of rodent in the genus Neotoma, but most commonly the bushy-tailed woodrat (Neotoma cinerea).
- One who tends to acquire various objects; one who collects, accumulates or has trouble throwing things away; a hoarder.
- To hoard things.