Middle Primitive Elvish
ari
noun. day
ar
root. day
n-
root. intensive
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A root in The Etymologies of the 1930s glossed “day” with various derivatives like ᴹQ. are, N. aur “day” and ᴹQ. arin “morning” (Ety/AR¹). In Tolkien’s later writings, the Quenya word for “day” became aurë (RC/727; S/190), and in 1957 Quenya Notes he devised a new etymology for these day-words from the root √UR “heat” as in ✶auri “heat, period of sun” (PE17/148). That opens the question whether the various 1930s Quenya “morning” words from ᴹ√AR remain valid, but many Neo-Quenya writers (including me) retain them since there aren’t really any good alternatives. They might be salvageable as derivatives of the later root √AS “warmth” (so that “day” = “hot” and “morning” = “warm”).