Meaning of -FOLD in English
~ combines with numbers to form adverbs which say how much an amount has increased by. For example, if an amount increases fourfold, it is four times greater than it was originally.
By the late eighties their number had grown fourfold...
Pretax profit surged almost twelvefold.
~ also combines with numbers to form adjectives.
One survey revealed a threefold increase in breast cancer.
ADJ: ADJ n
Collins COBUILD. Толковый словарь английского языка для изучающих язык Коллинз COBUILD (международная база данных языков Бирмингемского университета) . 2012