Pāṇini sūtras

The affix ṭhak optionally comes after the words ‘Phâlgunû’, ‘Sravanâ’, ‘Kartikû’ and ‘Chaitrû’ being the names of full moon nights, the whole word so formed being a Name denoting a division of time (a month, a fortnight or a year) in which the moon is full.

1. vibhāṣāविभाषा

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   vव्	vibhāṣविभाष्	vibhāṣāविभाषा	option	vibhāṣविभाष् + plus āआ

2. phālgunī+śravaṇā+kārtikī+caitrībhyaḥफाल्गुनी+श्रवणा+कार्तिकी+चैत्रीभ्यः

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   pप्	phālgunīफाल्गुनी	phālgunīफाल्गुनी	phālgunī [word]फाल्गुनी [wओर्द्]	phālgunफाल्गुन् + plus īई
   śश्	śravaṇश्रवण्	śravaṇāश्रवणा	śravaṇā [word]श्रवणा [wओर्द्]	śravaṇश्रवण् + plus āआ
   kक्	kārttikīकार्त्तिकी	kārtikīकार्तिकी	kārttikī [word]कार्त्तिकी [wओर्द्]	kārttikकार्त्तिक्
   cच्	caitrīचैत्री	caitrībhyaḥचैत्रीभ्यः	caitrī [word]चैत्री [wओर्द्]	caitrचैत्र् + plus ībhyaईभ्य

Anuvṛtti

1. sañjñāyāmसञ्ज्ञायाम् 4·2·21

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   sस्	saṃjñसंज्ञ्	sañjñāyāmसञ्ज्ञायाम्	name	saṃjñसंज्ञ् + plus āyआय्

2. ṭhakठक् 4·2·22

   Part	Lexeme	Sandhi form	Meaning	Stem
   ṭट्	ṭhakठक्	ṭhakठक्	ṭhakठक्	ṭhakठक्