A central plateau region of the Arabian Peninsula; formerly an independent sultanate until 1932 when it united with Hejaz to form the Kingdom of Saudi Arabia WordNet 3.0 & Open English WordNet

Najd, or the Nejd, forms the geographic center of Saudi Arabia, accounting for about a third of the country's modern population and, since the Emirate of Diriyah, acting as the base for all unification campaigns by the House of Saud to bring Arabia under a single polity and under the Salafi jurisprudence. Wikipedia

Central region of Saudi Arabia Wikidata

The central region of Saudi Arabia. Wiktionary