The Sindarin word for “now”, most notably appearing in the phrase annon edhellen, edro hi ammen “Elvish gate open now for us”. The exact form of this word is difficult to determine, since it is tied to Tolkien’s vacillations on how soft mutation functions in Sindarin grammar.

As originally conceived this word may have been tied to ᴹ√SI from the 1930s (Ety/SI), cognate to Q. sí “now”. As evidence for this see the phrases from the so-called Túrin Wrapper, where sí appears unmutated at the beginning of the phrase sí il chem en i Naugrim en ir Ellath thor den ammen but mutated to hí in ach hí in Ellath îr ed epholar after the conjunction ach. However, in Demonstrative, Relative, and Correlative Stems (DRC) from 1948 Tolkien had another demonstrative root ᴹ√KHI that (along with ᴹ√SI) “refers only to the actual present of the time of speaking” when used of time (PE23/96-97).

In notes on Words, Phrases and Passages from the Lord of the Rings (WPP) from the late 1950s or early 1960s, Tolkien said: “S. sī̆ ‘in this place (of speaker), here’. In Quenya sí means ‘now’ (cf. Galadriel's Lament); for which S. uses {hí >>} thí/hí” (PE17/27). In notes from the late 1960s, Tolkien said: “S. hē̆n, pl. hī̆n may be from sĭnā with generalized mutation of initial or from khĭn-, which appears in Q. hí here (S. sî here, hî now)” (VT49/34). However, in another note from the late 1960s, Tolkien gave S. sîr, sî as cognates to Q. sí, sír “now” (PE22/147).

Conceptual Development: The Gnomish Lexicon of the 1910s had G. cî {“now, at this moment” >>} “here” as an alternate to sî “here” (GL/26, 52), indicating the √SI vs. √K(H)I variations go back a long way.

Neo-Sindarin: For purposes of Neo-Sindarin, I assume the normal form is hí “now” < √KHI(N), shortened to hi when unstressed. I further assume that adverbs do not mutate after verbs to explain why the form doesn’t mutate to chí.