The most common and most likely answer to this crossword clue is the 9 letter word COLLECTOR
I've seen this crossword clue in The Daily Telegraph
C
O
L
L
E
C
T
O
R
Buddy explains!
The straight part
We know that "hoarder" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case hoarder = collector.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 COLLECTOR mean?
COLLECTOR noun- A person who or thing that collects, or which creates or manages a collection.
- A person who is employed to collect payments.
- The amplified terminal on a bipolar junction transistor.
- A compiler of books; one who collects scattered passages and puts them together in one book.
- One holding a Bachelor of Arts in Oxford, formerly appointed to superintend some scholastic proceedings in Lent.
- A major sewer which collects sewerage from a number of smaller branch sewers
- A mafioso whose task is to collect protection money from small businesses