N. [n] assimilated to following labial at morpheme boundaries; [n+{mb}] > [m+{mb}]

N. [n] assimilated to following labial at morpheme boundaries; [n+{mb}] > [m+{mb}]
GS/§4.121 @@@

Order (02000)

Before 02100 short final vowels vanished ON. Boronmíro/Borommíro > N. Boromir Ety/BOR
Before 05700 [mm] shortened ON. Boronmíro/Borommíro > N. Boromir Ety/BOR

Phonetic Rule Elements

[n+m] > [m+m]
[n+b] > [m+b]

Phonetic Rule Examples

lenbas > lembas n+b > m+b ᴹ√LEN > N. lembas ✧ EtyAC/LEN
boronmiro > borommiro n+m > m+m ON. Boronmíro/Borommíro > N. Boromir ✧ Ety/BOR