नडादीनां कुक् च

Operational rule vidhi

The augment कुक् comes after the words नड etc. when the affix छ follows in the above four senses.

Word by word (padaccheda)

Target नड- आदीनाम् ṣaṣṭhī · bahuvacanaSubstitute / term कुक् prathamā · ekavacanaIndeclinable च avyaya

Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.
Indeclinable An avyaya such as च "and", वा "optionally", न "not".

Dotted words are technical terms. Hover or tap one to see its card.

Full reading

नड-आदीनाम् कुक् च

Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.

As a rewrite rule (sketch from case endings)

नड- आदीनाम् → कुक्

Replace naḍa-ādīnām with kuk. Inherited words (anuvṛtti) may add further conditions.

Commentary

The augment कुक् comes after the words नड etc. when the affix छ follows in the above four senses.
To the words नड &c. the same affix is added, with the insertion of a क् after the stem. As नड + कुक् + छ = नडकीयम्; प्लक्षकीयम्, &c.
The words क्रुञ्चा and तक्षन् belong also to this class. In the case of क्रुञ्चा the long vowel is shortened, and in the case of तक्षन् the न् is elided : e. g. क्रुंचकीयम्, तक्षकीयम् ॥

1, नड, 2 प्लक्ष, 3 बिल्व, 4 वेणु, 5 वेत्र, 6 वेतस, 7 इक्षु, 8 काष्ठ, 9 कपोत, 10 तृण, 11क्रुञ्चा (क्रुञ्चाया) हृस्वत्वं च, 12 तक्षन् नलोपश्च.

Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.