The literal meaning is - अप्रत्यय: अणुदित् सवर्णस्य स्वस्य च. The following definitions are necessary for the sutra.
1. An अप्रत्यय is the de-suffixed part. For example, in इको यणचि, इक् is being de-suffixed i.e. replaced by the suffix यण्.
2. अण् is a प्रत्याहार
3. उदित् (उत् इत् ) implies "उत्s as इत् " - i.e. कु,चु,टु,तु,पु (5x5=25 letters)
The sutra implies that the de-suffixed parts and the अण्s would eclipse (or swallow if you will) their सवर्णs. For example, in रमा ईशः or माला छ (मालीयः), the आ is eclipsed.