I would like to ask if it is possible that the word pas, which I think could be a Sanskrit word, is a declined case of an existing word (e.g. the nominative or vocative case).
If not, could it be a word by itself (as is)?
According to this online dictionary, pas could be the nominative singular of pa or pā, but the declension of these words seems to be different, with the nominative ending with ḥ.
Sanskrit has two homophonic verbal roots pā, one meaning “to protect”, the other “to drink”. In both meanings they can occur as the second element of noun+verb compounds like nŗ-pa- “protecting men” or madhu-pa- “drinking honey”. As is normal in Sanskrit dictionaries, these words are cited as stems (without case endings); the nominative singular adds the ending -s (context form) or -ḥ (pausal form). pas and paḥ do not occur on their own as nouns, but they do occur in compounds.
In general, the nominative singular ending in Sanskrit is -ḥ. As @JanusBahsJacquet clarified, it derives from an earlier -s. However, -ḥ superficially manifests as such almost exclusively if the word to which it is added is an isolated word or if it ends the sentence. Whenever the next word in the sentence starts with a voiceless dental (i.e. t, th), then -ḥ reverts back to -s. This is part of a wider phenomenon known as external sandhi.
It is therefore possible, at least in theory, for a form lik paḥ to represent the nominative (from a root pa- or pas-).
