1》 consisting of two parts, elements, or aspects.
↘ Grammar denoting an inflection that refers to exactly two people or things.
2》 (often ~ to ) Mathematics related to another theorem or expression by the interchange of terms, such as ‘point’ and ‘line’.
1》 Grammar a ~ inflection.
2》 Mathematics a theorem or expression that is ~ to another.
■ verb ( ~s , ~ling , ~led ) Brit. convert (a road) into a ~ carriageway.
~ity noun ( plural ~ities ).
~ize or ~ise verb
ME: from L. ~is , from duo 'two'.