अन्तर्वत्पतिवतोर्नुक्

The augment नुक् is added to the words अन्तर्वत् and पतिवत् when the affix ङीप् is added to form the feminine.
This sutra points out the base and teaches the addition of the augment नुक् ॥ When this augment is added, (and it must be added at the end, by sutra 1.1.46), the forms become अन्तर्वत्न् and परिवत्न्; and these words must take nip by virtue of 4.1.5, if not by this sutra. Thus we have अन्तर्वत्नी and पतिवत्नी ॥ This irregular formation of the feminine is employed only then, when the sense of the words so formed is 'a pregnant female' and 'one whose husband is living' respectively. Therefore we have not the above forms in the following:- प्रथते त्वया पतिमती पृथिवी; here the word पतिमती qualifies the word पृथिवी and has not the sense of 'having the husband living', therefore its formation is regular. Similarly when the sense is not of 'a pregnant female', the feminine will not be अन्तर्वत्नी; in fact there will be no affixing of वत् (मतुप्). Because मतुप् is added to words possessing certain attribute, as described in 5.2.94, while the word अन्तर् has the sense of location, and can never be in apposition with the sense of अस्ति "having" as required by 5.2.94 The word अन्तर् would not therefore take मतुप् ॥ It does so irregularly by this sutra. The म is changed to व by 8.2.9 in अन्तर्वत् ॥ The change of म to व in पतिवत् is however irregular.

The augment नुक् is optionally added to these words in the Vedas:- as सान्तर्वत्नी or सान्तर्वती देवानुपैत् ॥ पतिवत्नी or पतिवती तरुणवत्सा ॥