Today we will look at the form पौत्रम् mAs from श्रीमद्भागवतम् verse 1.13.16.

युधिष्ठिरो लब्धराज्यो दृष्ट्वा पौत्रं कुलन्धरम् ।
भ्रातृभिर्लोकपालाभैर्मुमुदे परया श्रिया ∥ १-१३-१६ ∥

श्रीधर-स्वामि-टीका –
इदानीं राज्यस्यापकर्षं निरूपयितुमुत्कर्षं निगमयति – युधिष्ठिर इति । कुलन्धरं वंशधरम् ∥ १६ ∥

Gita Press translation “Having got back his kingdom and seen the face of a grandson capable of upholding the traditions of the family, Yudhiṣṭhira in his supreme splendor rejoiced with his younger brothers who were as powerful as the guardians of the various worlds (16).”

पुत्रस्यानन्तरापत्यम् (पुमान्) = पौत्रः – an immediate (male) descendant of a son = grandson (son’s son)
In the verses the विवक्षा is द्वितीया-एकवचनम्। Hence the form is पौत्रम्।

(1) पुत्र ङस् + अञ् । By 4-1-104 अनृष्यानन्तर्ये बिदादिभ्योऽञ् – Following a syntactically related पदम् in which the सन्धिः operations have been performed, and which ends in a sixth case affix and which has ‘बिद’ etc (listed in the बिदादि-गण:) as its base, the तद्धित: affix ‘अञ्’ may be applied optionally to denote the sense of
i) गोत्रापत्यम् (ref: 4-1-162 अपत्यं पौत्रप्रभृति गोत्रम्‌) of a sage
ii) अनन्तरापत्यम् (immediate descendant) of one who is not a sage.
As per the सूत्रम् 4-1-92 तस्यापत्यम् – Following a syntactically related पदम् in which the सन्धिः operations have been performed and which ends in a sixth case affix the तद्धिता: affixes already prescribed (by the prior rules 4-1-83 प्राग्दीव्यतोऽण् etc), as well as those that are going to be prescribed (by the following rules 4-1-95 अत इञ् etc), may be optionally applied to denote the sense of अपत्यम् (descendant.)

(2) पुत्र ङस् + अ । अनुबन्ध-लोपः by 1-3-3 हलन्त्यम्, 1-3-9 तस्य लोपः।

Note: ‘पुत्र ङस् + अ’ gets the designation प्रातिपदिकम्‌ by 1-2-46 कृत्तद्धितसमासाश्च। This allows 2-4-71 सुपो धातुप्रातिपदिकयोः to apply in the next step.

(3) पुत्र + 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) पौत्र + 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 ‘पौत्र’ gets the भ-सञ्ज्ञा by 1-4-18 यचि भम् which allows 6-4-148 यस्येति च to apply in the next step.

(5) पौत्र् + 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)।

= पौत्र । The प्रातिपदिकम् ‘पौत्र’ declines like राम-शब्दः।

(6) पौत्र + अम् । By 4-1-2 स्वौजसमौट्छष्टाभ्याम्भिस्ङेभ्याम्भ्यस्ङसिभ्याम्भ्यस्ङसोसाम्ङ्योस्सुप्‌।
Note: 1-3-4 न विभक्तौ तुस्माः prevents the ending letter ‘म्’ of the affix ‘अम्’ from getting इत्-सञ्ज्ञा।

(7) पौत्रम् । By 6-1-107 अमि पूर्वः – In place of a preceding अक् letter and the following vowel (अच्) belonging to the affix ‘अम्’ there is a single substitute of that preceding अक् letter.

We can similarly derive the following –
१) दुहितुरनन्तरापत्यम् (पुमान्) = दौहित्रः – an immediate (male) descendant of a daughter = grandson (daughter’s son)