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There are 3 typeas diad duad and dyad
duad, dual, guan, guar, luau, quad, quag, quai, quay, yuan
4-letter wordsadit, daut, dipt, dita, duad, duit, padi, paid, pita5-letter wordsaudit
3-letter words
add, dad, dud, tad, tat, tau, tut, uta
4-letter words
dada, data, daut, duad, taut, tutu
5-letter words
audad
Bisect (to divide into two parts), duplicate (to make an exact copy), duo (a pair of two), binary (relating to a system of two).