How can I make my axis title wider? The word wrapping breaks it into lines that are shorter than I want.

Prism's automatic word-wrapping feature may break axis titles into shorter segments than you want. You cannot adjust the size of the object, so you cannot adjust where Prism wraps to a second line. To work around this, select and delete the graph or axis title. Then create a new text object using the text tool:

When entering text into a text object, you have full control over line breaks.