"an egg with a double yolk"
"a double (binary) star"
"double doors"
"dual controls for pilot and copilot"
"duple (or double) time consists of two (or a multiple of two) beats to a measure"
"a double (or dual) role for an actor"
"the office of a clergyman is twofold; public preaching and private influence"
"every episode has its double and treble meaning"
"ancient Greek had the dual form but it has merged with the plural form in modern Greek"