The affix kyaṅ in the sense of becoming what the thing previously was not, is used after the crude forms bhṛś etc. which do not end with the affix cvi -- abhūtatadbhāve kṛbhvastiyoge sampadyakartari cviḥ [[5.4.50]], and there is lopa (elision) of the final consonant of these words, if they end in a consonant.,
Thus, अभृशो भृशो भवति = भृशायते 'he becomes much (from a little)'; शीघ्रायते 'he becomes swift (from being tardy)'. All these roots will be Atmanepadi 1.3.12.
The phrase अच्वेः 'not ending in the adverbial affix ई', refers to every one of the words belonging to the class भ्रिशादि. It may be objected, what was the necessity of adding this condition, since the affix च्वि itself denotes that something has become what it was not before; and therefore a word which has taken the affix च्वि, will not again take क्यङ् in that very sense. The repetition of च्वि here shows that the words भृश् &c. never take the affix च्वि, in the sense of 'something becoming what it was not before'. Thus the present sutra is an exception to sutra 5.4.50 which ordains च्वि.
भृशादिः
भृश्, शीघ्, मन्द, चपल, पण्डित, उत्सुक, उन्मनस्, अभिमनस्, सुमनस्, दुर्म्मनस्, रहस्, रोहस्, शश्वत्, वहत्, वहेत्, नृपत्, शुधि, अधर, ओजस्, वर्चस्, (विमनस्, रभन्, रोहत्, हन्, शुचिस्, अरजस्) ।,