"nine times repeated, nine times as great or numerous; consisting of nine parts," 1550s; see nine + -fold. Possibly a 16c. formation; the word is not attested in Middle English, but late Old English had nigonfeald.
my investment has increased ninefold
Nimrod
Nimzo-Indian
Nina
nincompoop
nine
ninefold
ninepence
ninepins
nines
nineteen
nineteenth