dually

Dually is an adverb meaning in two ways or twofold; it describes something that has two aspects, modes, or purposes. The form is derived from the adjective dual with the suffix -ly. In contemporary English, dually is relatively uncommon compared with phrases such as “in two ways” or “twofold,” and it is most often found in technical, philosophical, or formal prose.

Common uses describe mechanisms, policies, or relationships that operate or apply in two respects. Examples: The device can be used dually online and offline. The charger can operate dually on solar power and on the electrical grid. The policy applies dually to employees and contractors. Because of its rarity, writers frequently substitute clearer phrases like “in two ways” or “twofold” to avoid ambiguity.

Notes on style: Because dually can seem obscure, many editors prefer clearer wording such as “in two ways” or “twofold.” It is primarily used in formal or technical writing and should not be forced into casual prose. It is distinct from “dual,” which is an adjective describing two parts and would not typically serve as an adverb in the same sentence. See also duality, twofold, duplex.