It is believed that DR and CR are abbreviations of latin words, debit in latin is 'debere' (meaning 'to owe') and credit is 'credere' (meaning 'to believe').
There are other theories however. One is that DR stands for "debit record" and CR stands for "credit record". Another theory is that DR is short for "debtor" and CR is short for "creditor.
Hope this hope.