दिव उत्

For the final of the nominal-stem दिव् , there is the substitution of उ , when it is a पद (1.4.14 etc.).
The portion पद of the word पदान्त must be read into this sutra from 6.1.109. The word दिव् is here a nominal-stem and not a verbal-root. Thus दिवि कामो यस्य = द्युकामः, द्युमान्, विमलद्यु दिनं, द्युभ्याम्, द्युर्भिः ॥ We have said that दिव् is here a pratipadika and not a dhatu, for as a dhatu it ought to have its servile letter anubandha and should have been read as दिवु ॥ In the case of its being used as a verb, there takes place the substitution of long ऊ for व् by 6.4.19. In that case we shall have अक्षद्यूभ्याम्, अक्षद्यूभिः ॥ The उत् with a त् shows that short उ is meant, and debars ऊठ 6.4.19. In the case of ऊठ् substitution the forms will be द्यूभ्याम्, द्यूभिः ॥ The ऊठ् also comes because it is taught in a subsequent sutra. Why do we say 'when it is a Pada'? Observe दिवौ, दिवः ॥