consisting of or involving two parts or components usually in pairs(adj.all)
Example: An egg with a double yolk.
A double (binary) star.
Double doors.
Duple (or double) time consists of two (or a multiple of two) beats to a measure.
To increase by adding an equal number, quantity, length, value, or the like; multiply by two; as, to double a sum of money; to double a number, or length.(verb)
source: webster1913
To be increased to twice the sum, number, quantity, length, or value; to increase or grow to twice as much.(verb)