An adjective meaning “empty” attested only as an element in the Ilkorin name Mablosgen (Ety/MAP). As suggested by Helge Fauskanger, it might be a combination of Dor. lost and the adjective suffix -en, but if so it is unclear where the medial g came from (AL-Ilkorin/Mablosgen). Alternately, perhaps losgen is the general Ilkorin adjective for “empty” and lost is a variant used only in the Doriathrin dialect.
Doriathrin
caun
adjective. bowed, bow-shaped, bent
losgen Reconstructed
adjective. empty
lost Reconstructed
adjective. empty
A Doriathrin adjective meaning “empty” attested only as an element in the name Dor. Mablost (Ety/KAB). Its Quenya cognate lusta suggests a primitive form ✱✶lustā, with the [o] developing from Ilkorin a-affection. It might be a Doriathrin-only variant of more general Ilkorin losgen “empty”.
An adjective meaning “bowed, bow-shaped, bent” developed from the primitive form ᴹ✶kuʒnā (Ety/KUƷ). The middle diphthong went through various sound changes as indicated in The Etymologies. First the [[ilk|[u] became [o] preceding the final [a]]] (kogna), then the [[ilk|[g] (from ✶ʒ) vocalized to [u] before the [n]]] (coun) and finally the diphthong [[ilk|[ou] became [au]]] (caun).