The "r" in "Dr" for Debit

It's customary to write Debit on the Left side and Credit on the Right side in double-entry accounting system.

The difference between the total of all debits and the total of all credits is the "Balance". 
The genesis of these words dates back to a little over 500 Years and the credit goes to an Italian named Friar Luca-Pacioli.
Friar Luca-Pacioli. is the first to use the Latin terms
Credre  meaning "to entrust something"‘: Short form "Cr" and
Debere  meaning "to owe someone"  : Short form "Dr" 
(That's how "r" in Dr from Debere ).
Later, these words got transformed into ‘Debit and Credit’.