Historical background
Lenition refers to the mutation of medial consonants, occurring usually between two vowels (VCV). It affected the Old Sindarin sounds p, t, k, b, d, g, m and s.
The sounds w, kh were lenited only at the beginning of a word.
More specifically, the evolution of these sounds can be visualized in these examples:
- p > b
- OS *kelepe > S celeb "silver"
- t > d
- OS *atar > S adar "father"
- k > g
- OS beleka > S beleg "great"
- b > v
- OS *jabasse > S Iavas "autumn"[note 1]
- d > dh
- OS *badro > S badhor "brother"
- g > ∅
- OS *khugo > *huȝo[note 2] > S hû "dog"[note 1]
 In compounds
As a consequence, this process took place also in Old Sindarin compounds, when the initial letter of a word was no longer initial in a compound. Even in later compounds that would be pure Sindarin, the lenition was solidified as a rule, envisioning retroactively the lenition process from a theoretical Old Sindarin compound.
For example the word athrabeth "debate, converse (lit. 'across-word')" can be analyzed both as a derivative of OS word *athrapettha but also as a compound of Sindarin words athra- "across" + peth "word".
The fact that the above sounds mutated when medially was solidified as a rule
- thind + coll > Thingol (< ?OS *Thindakollo)
- cair + tân > Cirdan (< ?OS *Kiriatâno)
- fanui + dol > Fanuidhol (< ?OS *Fanoidolo)
- Edhel + sarn > Edhelharn (< ?OS *Edelosarno)
- har- + Gondor > Harondor (< ?OS *Kharagonddor)
- ar- + gwend > Arwen (< ?OS *Arwende; no g would evolve between ar- and wende)
- or- + hall > orchal (< ?OS *orkhalna; kh would not lenite as h inside a word)
 Grammatical and Syntactical significance
This article or section is a stub. Please help Tolkien Gateway by expanding it.
- Mutations in Sindarin by Thorsten Renk; it also covers Lenition.
- Soft mutation from the Ardalambion article on Sindarin by Helge Fauskanger
- Some Questions on Sindarin Lenition by Alfred W. Tueting