From Middle English -fold, -fald, -fauld, from Old English -feald (“-fold”), from Proto-Germanic *-falþaz (“-fold”), from Proto-Indo-European *-poltos (“-fold”), from *pel- (“to fold”). Cognate with Dutch -voud, German -fach, Swedish -faldig (“-fold”), Latin -plus, -plex, Ancient Greek -παλτος (-paltos), -πλος (-plos), -πλόος (-plóos). More at fold.
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- Used to make adjectives meaning times.
- There has been a threefold increase in inflation ( = inflation is three times what it was before)
- Used to make adverbs meaning times.
- Inflation has increased threefold ( = inflation is three times what it was before)
Note: -fold can be combined with the word for any positive integer. The words listed below are some of the most common combinations. These words are not hyphenated.
- Some writers and speakers use misconstructions like "an increase by twofold," which they believe to mean the same thing as "a twofold increase." But these two things logically mean "an increase by 200% of the original amount" and "an increase to 200% of the original amount," respectively. This practice is not only ambiguous but grammatically poor; it misuses -fold by using it as a noun. -Fold takes no preposition.
- In scientific contexts, "-fold" is sometimes appended to numerals (with the same sense), as in a 2010 paper by M.C. Stone et al., which mentions "10-fold up-regulation of the number of growing microtubules" in its abstract.