The opposite of increase is decrease or reduce.
increase
Decremental... meaning 'decrease'.
I'd say a "drastic decrease".
contract, decrease, diminish.
The opposite of acceleration is, Deceleration.
shrink, decrease in size, reduce
KK
The opposite of build (assemble) is to demolish or disassemble. The opposite of build (raise, increase) would be to decrease, lower, or reduce.
Decrease, Decline, Reduce and Deminish... Hope that Helps...
If that happens, the body's speed will decrease.
Shrinking young! ;P