What is the verb for largeness?

There isn't a single verb that directly translates to "largeness." "Largeness" is a noun describing a state of being large.

However, you can use verbs that relate to the idea of becoming larger or increasing in size:

* Expand: This implies growth in size or scope.

* Enlarge: This means to make something bigger.

* Grow: This refers to natural increase in size.

* Increase: This means to become greater in quantity or amount.

* Magnify: This implies making something appear larger.

The best verb to use depends on the specific context and what you want to emphasize.