The 7th king of Gondor (LotR/1038). His name seems to be a compound osto “city” and heru “lord”.

Conceptual Development: In the drafts of the Lord of the Rings appendices, Tolkien first gave his name as Ostohir, with a transient variation Ostonir (PM/197). Ostohir was a “mixed name” whose final element was Sindarin S. hîr “lord”, much like Ondohir which went through a similar conceptual development (PM/210). In the 2nd edition of The Lord of the Rings, Tolkien changed it to the pure Quenya name Ostoher.