"Subtrahend" is the name given to a number to be subtracted from another number.
5.8x - 2.3x = 3.5x
5.8x is the minuend.
2.3x is the subtrahend.
3.5x is the difference.
(9x + y) - (2x + 5y) = 7x - 4y
(9x + y) is the minuend.
(2x + 5y) is the subtrahend.
7x - 4y is the difference.