doubling the cube, a geometric problem

the assignment of a melody to two instruments in an arrangement

doubling time, the period of time required for a quantity to double in size or value.

syntactic doubling is a phenomenon consisting in the lengthening (gemination) of the initial consonant of certain words

in firearms, when more than one round is fired in a semiautomatic gas powered rifle with only one pull of the trigger, also known as a slam fire.

multiplication by 2

the composition or performance of a melody with itself or itself transposed at a constant interval such as the octave, third, or sixth