योगप्रमाणे च तदभावेऽदर्शनं स्यात्

And if the etymological meaning 'be held authoritative', then when such meaning is absent, the word also should vanish.
This sutra strengthens the former sutra. If it be said that a word always retains its etymological meaning in current language; then when there is an absence of such etymological meaning, then the word itself ought to vanish. But we know, as a matter of fact, that, there are words which have altogether lost their etymological sense, and connote a thing different from their radical meaning. Therefore to explain such words by lup elision of affixes is improper, because they do not retain the meaning of their primitive words.

It has already been said that words like पंचालाः &c. are not derivative words, &c. but are appellatives. If these words be taken as proving their etymological meaning, that is, as expressing or dependent upon, the sense of the original word, then when there is a loss of the original word signification, the secondary word must also cease to be employed. Thus if Panchalas be the name of the country in which the Kshatryas called Panchalas live, then when they cease to live in this country, it should cease to be called Panchalas. But we know, as a matter of fact, these words are now used without any reference to the people who once inhabited the countries. These words are consequently not derivative, but their sense is determined by usage. They are what may be called रूढि words.