Tenfold means by ten times as much. Increased tenfold, a tenfold rise, tenfold growth.
It multiplies rather than adds, which is the mistake people make with it: a tenfold increase is ten times the original, not eleven times, though careless writing sometimes means the second. It works as adjective and adverb without changing form. Note twofold, threefold, manifold, all built with the same old ending meaning times.
1adverbtenfoldBy ten times as much.
“Since the new road opened, traffic through the village has increased tenfold.”
tenfold is a multiple.
Old English tienfeald is ten plus -fold, an old ending meaning times. Manifold and twofold are built the same way.
Old English
tīenfeald
Middle English
tenfold
English, today
tenfold
From Middle English tenfold, tenfolde, from Old English tīenfeald, equivalent to ten + -fold.
Etymology from Wiktionary, CC BY-SA