The Cambridge Introduction to Sanskrit

Ṛ-STEMS

ṛ-stems are vowel-stems; but while most of the endings they employ have already been introduced in relation to other stems, the combination in which they use them is unique. Especially the singular needs to be memorised carefully. ṛ-stems display straightforward internal sandhi: the stem-final sound surfaces as vocalic -ṛ- between consonants and as consonantal -r- everywhere else. In final position, it changes into -ḥ in accordance with external sandhi. Like vant-/mant- and ant-stems (–› Chapter 25), ṛ-stems have stem gradation: their weak stems end in -ṛ, their strong stems (as before, used IN NOMVOCACC DU and PL and NOMVOC PL) in either guṇa -ar or vṛddhi -ār. Their LOC SG (!) stands in guṇa.

Most ṛ-stems actually end in -tṛ (guṇa -tar, vṛddhi -tār). They consist of two semantic groups: one group contains kinship terms, i.e. words denoting family relationships: मातृ- ‘mother’, पितृ- ‘father’, दुहितृ- ‘daughter’, or भ्रातृ- ‘brother’. The -tṛ/-tar in these is directly related to the -ther or -ter in the equivalent English words. The other, much larger group contains agent nouns. By taking a verbal root in guṇa and adding -tṛ, we get nouns such as ने-तृ- ‘leader’ (from √नी ‘to lead’), कर्-तृ- ‘doer, agent’ (from √कृ ‘to make, do’, e.g. in पाप-कर्तृ- ‘evil-doer’), लब्धृ- ‘taker’ (from √लभ् ‘to take’) etc. (The same internal sandhi applies as before -t- elsewhere; –› Chapter 8 and the Reference Grammar in Appendix III for details.) Some roots that end in consonants add not -tṛ, but -itṛ (as e.g. रक्षितृ- ‘protector’ from √रक्ष् ‘to protect’); generally speaking, -itṛ appears in those roots that also employ -itum (rather than -tum) to form their infinitive.

Four of the kinship terms (मातृ- ‘mother’, पितृ- ‘father’, दुहितृ- ‘daughter’ and भ्रातृ- ‘brother’) as well as नृ- ‘man’ behave as we might expect them to: their weak forms employ zero grade -tṛ, their strong forms guṇa -tar. All other kinship terms, as well as all agent nouns, employ not guṇa -tar, but vṛddhi -tār in their strong forms.