Reinvest earnings or profits in one's business, as in This company plows back half its profits every year. This term transfers the farming practice of turning the soil from top to bottom to financial enterprises. [First half of 1900s]
To reinvest some earnings or profits in one's business: After plowing back its profits for years, the company finally decided to pay dividends to its investors. The owners plowed the profits back into the business, using the money to buy new equipment.