Etymograph > Tolkien's Languages > Sindarin > Rules > s-nasal-mutation-phonemic

Source: https://eldamo.org/content/words/word-769508253.html

{p|t|k|h} > {f|θ|x|kh}
{b|d|g} > {m|n|ŋ} if next sound is not consonant

Referencing rules

s-nasal-mutation