Question

What is the other name negative acceleration ?

Answer 1

deceleration is the other name negative acceleration

Answer 2

Many have answered "deceleration" which is probably what you're looking for, but a negative acceleration doesn't necessarily mean something is slowing down. 

When a ball is dropped, we often use a negative acceleration to denote the fact that it is accelerating in the downward direction. It is, however, speeding up. 

I would say that an object slowing down is decelerating, but I wouldn't say an object decelerating necessarily has a negative acceleration. 

Negative acceleration really means accelerating in the negative direction. Maybe you can get a bonus for pointing this out.