An adjective meaning for “sparkling like jewels” (RGEO/64) in the poem A Elbereth Gilthoniel (LotR/238). It was the passive participle of the verb míria- “to sparkle like jewels” (PE17/24). Tolkien also considered connecting it to Quenya past passive participles like káriela in notes from 1969, perhaps from a verb ✱mir- with a Q. past participle míriela, but this Q. form was deleted and the whole thing seems to have been a transient idea (PE22/152).
Note: One of the forms from PE22 was published as mirieail, but Christopher Gilson confirmed in a Discord chat that the actual form was miriail: discord.com.
_adj. or quasi-adverb _like a jewel, shining jewel-like. In origin a participial form of verb míria-. silivren penna míriel lit. 'glittering slants-down sparkling (as jewels)'. >> míria-