Etymograph > Tolkien's Languages > Sindarin > Rules > s-i-affection-with-intrusion

Source: https://eldamo.org/content/words/word-2894407865.html

{a|o|u} > {e|e|y} if syllable is not last
{au|a|á|o|e|é} > {oe|ai|ai|y|i|í} if syllable is last
{ó|ú} > ui if number of syllables is 1

Referencing rules

s-plural