Second child of Tar-Súrion and younger brother of the second ruling queen of Númenor Tar-Telperien; his son Tar-Minastir inherited the throne after the queen died without children (UT/220). His name seems to be a compound Isil “moon” and the agental suffix -mo.

Conceptual Development: Very earlier in Tolkien’s legendarium, ᴱQ. Isilmo (QL/43) was given as the name of the son of ᴱQ. Isil (later ᴱQ. Inwe, Q. Ingwë).