The Sindarin word for “ear” was derived from primitive √S-LAS, an elaboration of √LAS “listen” (PE17/62). Its singular form lheweg is somewhat unusual. Based on its Quenya cognate Q. hlas (< ✶slas), its historical singular should probably be *lhâ. However, the modern Sindarin form was actually based on the (fossilized) dual lhaw < ✶slasū, from which a singular form lheweg “ear” was derived using the singular suffix -eg < -ikā (PE23/136), though it isn’t clear why the base vowel also changed from a to e since a-affection normally precedes (and prevents) i-affection.

The typical word for “ears” is the fossilized dual lhaw, but that can only be used to refer to the pair of ears on a single person, and this lhaw is treated as singular noun for purposes of verb and adjective agreement. When referring to multiple ears more generally, the plural lhewig is used (PE23/136).

Conceptual Development: Tolkien described a similar scenario in The Etymologies of the 1930s, except the singular was N. {lhaweg >>} lhewig and it was derived directly from ᴹ√LAS² “listen” (Ety/LAS²; EtyAC/LAS²). The voiceless lh- in this word was the result of the Noldorin sound-change of the 1930s whereby ancient initial r-, l- were unvoiced. This Noldorin dual lhaw made it into Lord of the Rings drafts as part of Amon Lhaw “Hill of Hearing, (lit.) of Ears” (TI/364), a form that Tolkien retained in the published version (LotR/393). Since the unvoicing of initial l was no longer a feature of Sindarin of the 1950s and 60s, Tolkien needed to contrive a new derivation from primitive √S-LAS.

The Gnomish word for “ear” from the 1910s had a completely different basis: it was G. unc “ear, handle (of a jar)” (GL/75), cognate to ᴱQ. unk derived from the root ᴱ√ṆQṆ² (QL/98).