Today we will look at the form पितामही fNs from श्रीमद्भागवतम् Sb9.24.55.

अष्टमस्तु तयोरासीत्स्वयमेव हरिः किल ।
सुभद्रा च महाभागा तव राजन्पितामही ∥ ९-२४-५५ ∥

श्रीधर-स्वामि-टीका
अष्टमस्तु स्वयमेवासीन्नतु कर्मादिना हेतुना ताभ्यां जनितो वा, यतोऽसौ हरिः ∥ ५५ ∥

Gita Press translation- While the eighth son of (the blessed) Vasudeva and Devakī indeed was Lord Śrī Hari Himself. And the highly blessed Subhadrā, your grandmother was their daughter, O king! (55)”

पितुर्माता = पितामही – grandmother (father’s mother)

First, we derive the masculine form ‘पितामह’ as follows –

(1) पितृ ङस् + डामहच् । By 4-2-36 पितृव्यमातुलमातामहपितामहाः – The forms ‘पितृव्य’, ‘मातुल’, ‘मातामह’ and ‘पितामह’ are given as ready-made forms. They are used in the meaning of ‘father’s brother’, ‘mother’s brother’, ‘mother’s father’ and ‘father’s father’ respectively.
Note: As per the वार्तिकम् ‘मातृपितृभ्यां पितरि डामहच्’ – The affix ‘डामहच्’ is to be applied to get the final forms ‘पितामह’ and ‘मातामह’ (listed in the सूत्रम् 4-2-36) – which denote father’s father and mother’s father respectively.

(2) पितृ ङस् + आमह । अनुबन्ध-लोपः by 1-3-3 हलन्त्यम्, 1-3-7 चुटू, 1-3-9 तस्य लोपः।

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

(3) पितृ + आमह । 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 ‘डामहच्’ is a डित् (has the letter ‘ड्’ as a इत्) and the अङ्गम् ‘पितृ’ gets the भ-सञ्ज्ञा by 1-4-18 यचि भम्। This allows 6-4-143 टेः to apply in the next step.

(4) पित् + आमह । By 6-4-143 टेः – When the अङ्गम् has the भ-सञ्ज्ञा, then its टि-portion (ref: 1-1-64 अचोऽन्त्यादि टि) takes लोप: when followed by an affix that has the letter ‘ड्’ as an indicatory letter.

= पितामह ।

Now we apply the appropriate feminine affix.

(5) पितामह + ङीष् । By 4-1-41 षिद्गौरादिभ्यश्च – In the feminine gender the affix ‘ङीष्’ is prescribed following a प्रातिपदिकम् which either (i) contains the letter ‘ष्’ as a ‘इत्’ or (ii) belongs to the class of words beginning with ‘गौर’।
Note: The affix ‘डामहच्’ is considered to be a षित् (having the letter ‘ष्’ as a इत्) as per the वार्तिकम् (under 4-2-36 पितृव्यमातुलमातामहपितामहाः) ‘मातरि षिच्च’ – When used in the sense of a mother, the affix ‘डामहच्’ (implied by the ready-made forms ‘मातामह’ and ‘पितामह’ listed in the सूत्रम् 4-2-36) is considered to be a षित् (having the letter ‘ष्’ as a इत्)। This enables 4-1-41 षिद्गौरादिभ्यश्च to apply.
Note: Some grammarians consider the forms ‘मातामह’ and ‘पितामह’ as belonging to the गौरादि-गणः, which enables the application of the सूत्रम् 4-1-41 षिद्गौरादिभ्यश्च। Hence according to them the वार्तिकम् ‘मातरि षिच्च’ is not necessary.

(6) पितामह + ई । अनुबन्ध-लोपः by 1-3-3 हलन्त्यम्, 1-3-8 लशक्वतद्धिते , 1-3-9 तस्य लोपः।

Note: The अङ्गम् ‘पितामह’ has the भ-सञ्ज्ञा here as per the सूत्रम् 1-4-18 यचि भम्। This allows the सूत्रम् 6-4-148 यस्येति च to apply in the next step.

(7) पितामह् + ई । 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)।

= पितामही । The प्रातिपदिकम् ‘पितामही’ declines like नदी-शब्द:।

Similarly, we can derive the form –
१) मातुर्माता = मातामही – grandmother (mother’s mother)