Old English feowerfeald; see four + -fold. As an adverb from 1530s. Similar formation in Old Frisian fiuwerfald, Dutch viervoudig, Old High German fiervalt, German vierfältig, Danish firfold, Gothic fidurfalþs.
a fourfold increase in the dosage
the price of gasoline has increased fourfold over the past two years
fourchette
four-corners
four-door
four-eyes
four-flusher
fourfold
four-footed
Fourierism
four-poster
fourscore
foursome
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