Part of speech: Adverb
by a factor of four
Example: the price of gasoline has increased fourfold over the past two years
Four-fold, Fourfold, Quadruple, Quadruplicate, Quadruplex
The word "fourfold" comes from Old English fΔowerfeald, which comes from Middle English fourfold. Many other languages have similar words:
four β A related word in the same word family.
fold β A related word in the same word family.
Old English was a fully Germanic language before the Norman Conquest transformed it.