Today we will look at the form पाञ्चाल mVs from महाभारतम् verse 1-195-19.

व्यास उवाच
अनृतान्मोक्ष्यसे भद्रे धर्मश्चैष सनातनः ।
न तु वक्ष्यामि सर्वेषां पाञ्चाल शृणु मे स्वयम् ॥ १-१९५-१९ ॥

Translation – O blessed one (Kuntī), you shall be saved from untruth. This is eternal virtue. But, O Pāñcāla (Drupada – a king of the territory Pañcāla), I will not speak (about this matter) to all. You alone listen to me (19).

पञ्चाला जनपदः, पञ्चालो नाम क्षत्रियः। पञ्चालानां राजा = पाञ्चालः – king (Drupada) of the territory Pañcāla, which is also the name of a kṣatriya.
Note: As a convention in the language, words (such as ‘पञ्चाल’) while denoting a territory are always used in the plural.

In the verses the विवक्षा is सम्बुद्धिः। Hence the form is (हे) पाञ्चाल।

(1) पञ्चाल आम् + अञ् । By 4-1-168 जनपदशब्दात्‌ क्षत्रियादञ् – To denote the sense of अपत्यम् (descendant) the तद्धित: affix ‘अञ्’ may be applied optionally following a syntactically related पदम् which ends in a sixth case affix and has as its base a word that denotes the name of a kṣatriya king, as well as the name of his country/territory.
As per the वार्तिकम् (under the सूत्रम् 4-1-168 जनपदशब्दात्‌ क्षत्रियादञ्) ’क्षत्रियसमानशब्दाज्जनपदात् तस्य राजन्यपत्यवत्’ – The same तद्धित: affix as is used to denote a descendant, may also be used to denote a king, when applied following a syntactically related पदम् which ends in a sixth case affix and has as its base a word that denotes the name of a country/territory, as well as the name of a kṣatriya.
Note: The सिद्धान्तकौमुदी says, तद्राजमाचक्षाणस्तद्राज इत्यन्वर्थसंज्ञासामर्थ्यात् – The above वार्तिकम् is inferred from the fact that the affixes ‘अञ्’ etc (prescribed by 4-1-168 etc) get the designation तद्राजाः (explained as तेषां राजानस्तद्राजाः) by the सूत्रम् 4-1-174 ते तद्राजाः, which implies that these affixes are also used to denote kings (of those countries/territories).
Note: The तत्वबोधिनी says, इह ‘4-2-125 अवृद्धादपि बहुवचनविषयात्’ इति प्राप्तो वुञ् बाध्यते – Here, the affix ‘अञ्’ stops the affix ‘वुञ्’ which would have been prescribed by the सूत्रम् 4-2-125 अवृद्धादपि बहुवचनविषयात्।

(2) पञ्चाल आम् + अ । अनुबन्ध-लोपः by 1-3-3 हलन्त्यम्, 1-3-9 तस्य लोपः।
Note: ‘पञ्चाल आम् + अ’ gets the designation प्रातिपदिकम्‌ by 1-2-46 कृत्तद्धितसमासाश्च। This allows 2-4-71 सुपो धातुप्रातिपदिकयोः to apply in the next step.

(3) पञ्चाल + अ । By 2-4-71 सुपो धातुप्रातिपदिकयोः – A सुँप् affix takes a लुक् elision when it is a part of a धातुः or a प्रातिपदिकम्।

Note: The affix ‘अञ्’ is a ञित् (has the letter ‘ञ्’ as इत्)। This allows 7-2-117 तद्धितेष्वचामादेः to apply in the next step.

(4) पाञ्चाल + अ । By 7-2-117 तद्धितेष्वचामादेः – The first vowel among the vowels of a अङ्गम् which is followed by a तद्धित: affix (ref. 4-1-76 तद्धिताः) which is either a ञित् (has the letter ‘ञ्’ as a इत्) or a णित् (has the letter ‘ण्’ as a इत्) takes the वृद्धि: (ref. 1-1-1 वृद्धिरादैच्) substitute.
Note: The अङ्गम् ‘पाञ्चाल’ gets the भ-सञ्ज्ञा by 1-4-18 यचि भम् which allows 6-4-148 यस्येति च to apply in the next step.

(5) पाञ्चाल् + अ । By 6-4-148 यस्येति च – When the letter ‘ई’ or a ‘तद्धित’ affix follows, the (ending) इ-वर्ण: (letter ‘इ’ or ‘ई’) or the (ending) अवर्ण: (letter ‘अ’ or ‘आ’) of the अङ्गम् with the भ-सञ्ज्ञा takes elision (लोपः)।

= पाञ्चाल । Note: The प्रातिपदिकम् ‘पाञ्चाल’ declines like राम-शब्दः।