Pāṇini sūtras

The affix ṭach comes after the word uras standing at the end of a Tatpurusha compound, when it has the sense of ‘the most excellent of its kind’.

1. agra+ākhyāyāmअग्र+आख्यायाम्

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	agraअग्र	agraअग्र	acme	agrअग्र् + plus aअ
   āआ	ākhyāआख्या	ākhyāyāmआख्यायाम्	name	ākhyआख्य् + plus āyआय्

2. urasaḥउरसः

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   uउ	urasउरस्	urasaḥउरसः	uras [word]	urउर् + plus asaḥअसः

Anuvṛtti

1. samāsa+antāḥसमास+अन्ताः 5·4·68

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   sस्	samāsaसमास	samāsaसमास	Sanskrit compound	samāsसमास् + plus aअ
   aअ	antaअन्त	antāḥअन्ताः	end	antअन्त् + plus āMआM

2. tatpuruṣasyaतत्पुरुषस्य 5·4·86

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   tत्	tatpuruṣaतत्पुरुष	tatpuruṣasyaतत्पुरुषस्य	tatpuruṣaतत्पुरुष	tatpuruṣतत्पुरुष् + plus asyaअस्य

3. ṭacटच् 5·4·91

   Part	Lexeme	Sandhi form	Meaning	Stem
   ṭट्	ṭacटच्	ṭacटच्	ṭacटच्	ṭacटच्