MORTGAGE. This term occurs just once in the KJV (Neh 5:3): “There were also those who said, ‘We are mortgaging our fields, our vineyards and our houses’...”—in a time of drought and want. The verb is ’ārab, which is used of pledging or pawning personal property in all other passages, but here of real estate, which is put up as collateral for a loan. The root basically refers to exchanging or trading merchandise (the verb is so used in Ezek 27:9, 27), but it also can be used of becoming surety or guarantor of a loan made to some borrower. The related nouns are ’arubbāh (“surety, pledge”—1 Sam 17:18) and ’ērābōn (“a guarantee, pledge”—a term which was borrowed by Koiné Gr. as arrabōn, meaning “first installment, down payment, pledge,” applied to the Holy Spirit as the “earnest” of the believer’s heavenly inheritance in 2 Cor 1:22; Eph 1:14). Although the technical term for mortgaging real property occurs only once (Neh 5:3 above cited), there can be no question that this was a much-practiced mode of securing loans from the time of the Heb. conquest and onward. According to the Pentateuch, one of the duties of the kinsman redeemer (gō'ēl) was to redeem the mortgaged property of his indigent relative. This was one of the services performed by Boaz for Naomi, his dead kinsman’s widow (in addition to his levirate marriage of Ruth).

International Standard Bible Encyclopedia (1915)

To give or be security as a part of bartering, give pledges, become surety. In time of great need for food, "Some also there were that said, We are mortgaging (the King James Version "have mortgaged") our fields," etc. (Ne 5:3).

See Surety.