सूत्रस्थितानां वर्णानामर्थानां च प्रतीतये ।
विशुद्धा चाधिका व्याख्या वृत्तिरुक्ता मनीषिभिः ॥
sūtra-sthitānāṁ varṇānām arthānāṁ ca pratītaye |
viśuddhā cādhikā vyākhyā vṛttir uktā manīṣibhiḥ ||
(Unknown source; cited in the Amṛta-ṭīkā on Hari-nāmāmṛta-vyākaraṇa: 155)
“A carefully formulated additional explanation [of a sūtra] for the purpose of ascertaining the phonemes and meanings present in a sūtra is called a vṛtti by the wise.”