The Quenya word for “eye”, derived from the root √KHEN for eye-words (PE17/187; Ety/KHEN-D-E) and with stem-form hend- given its dual hendu (WJ/337).
Conceptual Development: This word first appeared as ᴱQ. hen in The Qenya Phonology of the 1910s, derived from primitive ᴱ✶þχe-ndǝ and appearing beside ᴱQ. sé “eye, pupil” < ᴱ✶þeχē (PE12/21). Hen (hend-) “eye” appeared in the Qenya Lexicon though it was marked “†” for archaic (QL/40), and ᴱQ. hend- also appeared in the contemporaneous Gnomish Lexicon as the cognate of G. hen “eye” (GL/48). ᴱQ. hen appeared regularly in documents from the 1920s (PE13/147; PE14/43, 76; PE16/136), although in the Early Noldorin Grammar of the 1920s ᴱQ. sinda was given as the cognate of ᴱN. hen(n) “eye” (PE13/122). The form ᴱQ. sinda seems to have been a transient idea.
A lengthy declension of ᴹQ. hen “eye” appeared in documents from the early 1930s (PE21/52) and in The Etymologies of the 1930s it was based on a new the root ᴹ√KHEN-D-E “eye” (Ety/KHEN-D-E). In both these documents, inflected forms indicate a stem form of hend-. Thus this word and its stem were quite stable in Tolkien’s mind, though he did alter its root from early ᴱ√SEHE [ÞEHE] to later √KHEN.
hen (hend-, as in pl. hendi) noun "eye" (KHEN-D-E); possibly dual #hendu in hendumaica, q.v. Noun henfanwa "eye-screen, veil upon eyes" (PE17:176), adj. henulca "evileyed" (SD:68; cf. ulca).