From www.thefreedictionary.com dy·ad (dd, -d) n. 1. Two individuals or units regarded as a pair: the mother-daughter dyad. 2. Biology One pair of homologous chromosomes resulting from the division of a tetrad during meiosis. 3. Chemistry A divalent atom or radical. 4. Mathematics a. A function that draws a correspondence from any vector u to the vector (v·u)w and is denoted vw, where v and w are a fixed pair of vectors and v·u is the scalar product of v and u. For example, if v = (2,3,1), w = (0,-1,4), and u = (a,b,c), then the dyad vw draws a correspondence from u to (2a + 3b + c)w. b. A tensor formed from a vector in a vector space and a linear functional on that vector space. adj. Made up of two units.