Having Latin roots, the term "debit" comes from the word "debitum", meaning "what is due", and "credit" comes from "creditum", defined as "something entrusted to another or a loan".
One theory asserts that the DR and CR come from the Latin past participles of debitum and creditum which are "debere" and "credere", respectively. Another theory is that DR stands for "debit record" and CR stands for "credit record". Finally, some believe the DR notation is short for "debtor" and CR is short for "creditor".