There isn't a single perfect opposite of a meander in geological terms. This is because "meander" describes a specific type of river channel formation, and its "opposite" would depend on what aspect of the meander you're contrasting.

Here are a few possible interpretations and their "opposites":

1. Straightness: If you consider the curvature of a meander, its opposite would be a straight river channel. This is common in areas with strong bedrock, steep slopes, or where recent geological activity has altered the river course.

2. Erosional vs. Depositional: Meanders are characterized by erosion on the outer bank and deposition on the inner bank. So, a straight channel with uniform erosion or deposition along its sides could be considered an opposite.

3. Dynamic vs. Static: Meanders are dynamic, constantly changing over time. A stable, unchanging river channel with little to no erosion or deposition could be viewed as its opposite.

4. Channel Form: If you're focusing on the sinuous shape of a meander, then the opposite would be any channel form that is not sinuous, like a braided channel, a straight channel, or a canyon.

Ultimately, the "geological opposite" of a meander depends on the specific aspect you're comparing. It's more helpful to consider the characteristics of a meander and find contrasting features in other river channel types.