Which term describes a reduction in the contexts a word can appear in?

Narrowing is the correct term that describes a reduction in the contexts a word can appear in. This linguistic phenomenon occurs when a word that once had a broader meaning becomes more specific over time. For instance, the word "meat" originally referred to any kind of food but has now narrowed to specifically denote animal flesh.

In this context, narrowing helps illustrate how language evolves, becoming more precise in its usage. As words undergo this change, they lose some of their broader applications, thereby affecting how they can be used in different contexts. Understanding narrowing is essential for grasping how language shifts in meaning over time.