Istar noun "Wizard", used of Gandalf, Saruman, Radagast etc. Pl. Istari is attested. Gen. pl. in the phrase Heren Istarion "Order of Wizards" (UT:388). "The istari are translated wizards because of the connexion of wizard with wise and so with witting and knowing" (Letters:207); by this translation Tolkien tries to reproduce the relationship between Quenya istar and ista- #1, 2.
Quenya
istar
proper name. Wizard, (lit.) One Who Knows
Istar
wizard
ista
knowledge
ista (1) noun "knowledge" (IS). Also istya.
istare
noun. knowledge
istya
knowledge
istya noun "knowledge" (IS). Also ista (#1).
curuvar
wizard
curuvar _("k")_noun "wizard" (LT1:269 but Gandalf, Saruman etc. were istari)
Nolmë
knowledge, philosophy (including science)
Nolmë ("ñ")noun "knowledge, Philosophy (including Science)" (PM:360 cf. 344)
handë
knowledge, understanding, intelligence
handë noun "knowledge, understanding, intelligence" (KHAN). Note: *handë is (probably) also the past tense of the verb har- "sit".
issë
knowledge, lore
issë noun "knowledge, lore" (LT2:339; rather ista or istya in Tolkien's later Quenya)
sairon
wizard
sairon noun "wizard" (SAY); according to LT2:337 and GL:29, Sairon is also the Quenya (or Qenya) name of Dairon (Daeron).
A name for the five Wizards who travelled from the West to aid the free peoples against Sauron (LotR/1084, UT/388). It usually appeared in its plural form Istari, which meant “those who know” (Let/202, PM/360). Tolkien generally translated the name as “Wizard”, because the Old English sense of word was similar to the true meaning of this Quenya word (Let/207). The name Istar was most likely a combination of the verb ista- “to know” and the old agental suffix -r(o).
The title Istar was not used for ordinary mortal “wizards” or “magicians” (UT/388). For this purpose, perhaps the word [ᴹQ.] sairon was used instead.