Q:
Where does the Russian word сундук (soondúk = trunk, chest, as in treasure chest) come from?
A:
It's probably from Arabic صَنْدُوْق (Sanduuq = box, bin, money box, fund)! I would guess it came into Arabic from Persian (it's not at all a typical Arabic word, and resembles other Persian loanwords).
And according to this site, the word made into Russian through the Tatar language.
And the primary origin? This etymological list claims it came into Persian from a Greek word, but I haven't yet found any other references.
Q:
How/why did I get started on this, anyway?
A:
About an hour ago, I was studying for an Arabic final by reading through part of a reference grammar, and came across صندوق in an example sentence. You can guess how quickly my studying is going.