When searching for alternative words for the phrase "most deterrent," there are several options available. The term "most discouraging" is often used to describe something that has a strong negative impact on a particular behavior or action. "Greatest dissuasive" is another phrase that can be used to convey the idea of something being highly effective at discouraging a certain action. Additionally, "most preventive" is a term that can be used to describe something that helps to avoid a particular problem or issue. Other options include "most inhibiting," "most restraining," or "most obstructive." Ultimately, the choice of words will depend on the particular situation and the desired tone and emphasis of the statement.