The proper Sindarin name of NS. Hithlum (itself North Sindarin), since in Western Sindarin phonology a primitive [[s|final [m] became a nasalized [v]]], which was then absorbed by the preceding [u] (PE17/133).
Conceptual Development: A form N. Cílu appearing linguistic notes from the 1930s might be an early “true Noldorin” name for Hithlum (PE21/32).
topon. pure Sindarin form of Hilthlum.