Which action refers to making something wider or larger?

The action of making something wider or larger is best described by the term "dilate." In a physiological context, dilation refers to the process of widening or expanding, such as the dilation of pupils in response to low light conditions, allowing more light to enter the eye. This term is frequently used in medical and biological discussions, where various structures of the body expand to accommodate different needs, such as increased blood flow or airflow.

The other terms have distinct meanings: to dilute means to reduce the concentration of a substance, typically by mixing it with a solvent; to deter refers to preventing someone from taking an action, usually by instilling doubt or fear; and to dissuade involves persuading someone not to do something. All these terms convey concepts related to reduction or influence rather than the expansion implied by dilation. Hence, in the context of making something wider or larger, "dilate" is the most appropriate choice.