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 [u] became [o] preceding the final [a] (kogna), then the [g] (from ✶ʒ) vocalized to [u] before the [n] (coun) and finally the diphthong [ou] became [au] (caun).
caunadjective. bowed, bow-shaped, bent
* lostadjective. empty
* losgenadjective. empty
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.