Find the Opposite Number: Converting -18 to Its Inverse

To solve this problem, we need to find the opposite number of $-18$.

Typically, the opposite of a number refers to its additive inverse, which would be $18$. However, based on the problem context and subject information (determine the reciprocal), we interpret the task as finding the opposite reciprocal.

• Step 1: Identify the given number, which is $-18$.
• Step 2: Calculate the reciprocal of $18$, the positive component. The reciprocal of $18$ is $\frac{1}{18}$.
• Step 3: Since the original number is negative, the reciprocal also changes sign, becoming: $-\frac{1}{18}$.

Hence, the opposite number of $-18$ considering the reciprocal context is $-\frac{1}{18}$.

Therefore, the final answer is $-\frac{1}{18}$.