The term "opposite" probably refers the the value which is the distance from 0 on the numberline, but on the opposite side.
The opposite of
This is also known as the 'additive inverse'
Additive inverses have the property that their sum is 0.
The 'reciprocal' of a number is the number 'turned upside down'.
It is also known as the multiplicative inverse.
Reciprocals have the property that their product is equal to 1.