Pāṇini sūtras

And so also a feminine word, ending with a vrṛiddha affix, when similarly spoken along with the same word but which ends with a yuvan affix, is only retained; and it is treated like a masculine.

German Wenn der Vṛddha genannte Geschlechtsname ein Femininum ist, dann bleibt dieses allein übrig, nimmt aber die Form des Masculinums an. (66)

1. strīस्त्री

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   sस्	strīस्त्री	strīस्त्री	feminine	strस्त्र् + plus īई

2. pum+vat+caपुम्+वत्+च

   Part	Lexeme	Sandhi form	Meaning	Stem
   pप्	puṃsपुंस्	pumपुम्	masculine	puṃsपुंस्
   vव्	vatवत्	vatवत्	equally	vatवत्
   cच्	caच	caच	besides	caच

Anuvṛtti

1. viśeṣaḥविशेषः 1·2·65

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   vव्	viśeṣaविशेष	viśeṣaḥविशेषः	distinction	viśeṣविशेष् + plus aḥअः