2,797. When Terms Are Used in Two Different Ways

Hilchos Nedarim 9:4

If some people refer to a food in one way and others don’t, we don’t follow the majority practice. Rather, it is considered a doubt vis-à-vis a vow, and we rule stringently in cases of doubt regarding a vow. However, if one violates such a vow, he isn’t liable to lashes.

Hilchos Nedarim 9:5

Pursuant to the previous halacha, let’s say that someone made a vow prohibiting oil in a place where people use both olive oil and sesame oil. Most of the locals use the generic term “oil” to mean olive oil, and they call sesame oil “sesame oil.” Some locals, however, also call sesame oil just plain “oil.” In such a circumstance, the one who vowed is prohibited both oils, but he’s not liable to lashes if he eats sesame oil. The same is true in all similar situations.