This name was given to two different women in Tolkien’s legendarium. First, it was the name of the first wife of Finwë, the mother of Fëanor (S/63). She was the first Elf to die a non-violent death, for which she was also called Fíriel “She that Sighed, She that Died” (MR/250). The second woman, Tar-Míriel, was the Quenya name of the queen of Númenor, also known as Ad. Ar-Zimraphel (S/269, UT/224). The first element of this name is almost certainly mírë “jewel”. The second element is the suffix -iel, which either means “-daughter” or is a general feminine suffix.
Conceptual Development: The first name given to the last queen of Númenor was ᴹQ. Istar >> Tar-Ilien (LR/27).
Míriel noun "Jewel-woman" or "Jewel-daughter" (Silm), genitive Míriello (see namna) indicating a stem-form #Míriell-.