Relating to or involving the number two or a pair of things; having two-fold properties or characteristics.
From Latin duo, 'two' plus -dial (possibly related to dial, but more likely from Latin -alis, an adjectival suffix). The term suggests duality or twofold nature, though it's rarely used in modern English.
This word appears mostly in physics and electronics contexts from the early-to-mid 20th century, where scientists used it to describe devices or properties involving dualities—it's become somewhat obsolete as more precise technical terminology developed.
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