twofold

Twofold is an English adjective and adverb meaning double or consisting of two parts. It indicates something is twice as much or has two components, and can describe both quantitative increases and qualitative dual aspects. The term is formed from two and fold, with fold historically tied to multiplicity or repetition.

As an adjective, twofold describes something with two aspects or forming a pair. As an adverb, it describes doubling in extent or frequency, as in a twofold increase or costs that have risen twofold. The expression appears across everyday language and more technical contexts.

In various disciplines, twofold appears in distinct senses. In geometry and biology, twofold symmetry refers to an object that is invariant under a 180-degree rotation. In chemistry and crystallography, it can describe a twofold rotation axis. In economics or statistics, a twofold increase denotes a doubling of a quantity. The usage is common with numeric modifiers (twofold, threefold, etc.) and contrasted with onefold or multi-fold in emphasis.

Twofold is related to synonyms such as double, dual, and twin, while antonyms include single or onefold. Its etymology traces the combination of two with fold to express multiplicity, a pattern that recurs in related terms like twofold, threefold, and multfold.