An archaic dvanda dual form in the Early Qenya Grammar of the 1920s referring to both parents based on older atta(h)-, replaced by the dual atarqi of ᴱQ. atar in normal speech (PE14/77). As a dvanda dual, it was based on the word for “father”, with “mother” being implied. It also appeared in an (archaic?) plural form attahi in the English-Qenya Dictionary, but presumably this only meant “fathers” (PE15/72).
Early Quenya
nosta
noun. birth, birthday
nosta-
verb. to give birth to; to cause
nostale
noun. species, kind; nature
nostalen mára
good by nature
attahwi
noun. parents
puita-
verb. to beget
A noun appearing as ᴱQ. nosta “birth, birthday” in the Qenya Lexicon of the 1910s derived from the early root ᴱ√NŌ “become, be born” (QL/66).
Neo-Quenya: As the root √NŌ survived in Tolkien’s later writings with very similar meanings, I’d retain ᴺQ. nosta for purposes of Neo-Quenya, but I’d limit its use to “birth”, and for “birthday” I’d use ᴺQ. nostarë.