It was not a lot, but it had not been touched in the meantime and some interest had accumulated.
Besides that, they had not been using up all the money that Gregor had been bringing home every month, keeping only a little for himself, so that that, too, had been accumulating.
There are no more uses of "accumulate" in the book.
Show samples from other sources
Dr. Finch became a bone man, practiced in Nashville, played the stock market with shrewdness, and by the time he was forty-five he had accumulated enough money to retire and devote all his time to his first and abiding love, Victorian literature, a pursuit that in itself earned him the reputation of being Maycomb County’s most learned licensed eccentric.
Harper Lee -- Go Set a Watchman
Thomas kept coughing and rubbing chunks of accumulated grime from the corners of his eyes.