If I lend an amount of $100 to my friend, I can refer to the amount as receivable. Suppose she returns $100 (or $70) after one week, what should I call this amount? It is the "return amount which is borrowed"?
Any money that is paid back to you is a payment or a remittance.
In terms of how the money is applied to the debt, it may be principal if it is against the amount originally borrowed, or it may be interest if it is part of the fee you may have charged your friend for the trouble of loaning the money.