retain

“retain” is a more formal way of saying ‘keep’. It’s especially common in phrases like “to retain control / status / a position” etc. The noun is “retention”. It’s also used in a physical sense to mean “keeping something inside”. In business, retention is very important, because companies need to try to keep the customers they already have as well as trying to attract new ones.

He was unable to  retain control of the company after he had lost the confidence of investors

She explained her weight gain as the result of fluid retention.