لو حلف «لا يأكل بيضاً» كان ذلك على المتعارف
If a person swears not to eat eggs, the oath is assessed according to recognized use.
فلا يحنث بتناول بيض العصفور والحمامة
In the usage assumed by the example, eating sparrow or pigeon eggs does not violate it.
The lexical category *eggs* includes many birds' eggs, while the ordinary food term may identify a much narrower class. The interpreter must therefore distinguish linguistic possibility from established intended usage.
Two questions matter: What can the word denote lexically? What does this community understand by the word in this setting? They need not have identical answers.
Since custom can vary by time and place, the historically assumed usage should not be applied mechanically to every contemporary situation.