Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Mŏnoecus, i, m., = Μόνοικος (that dwells alone), a surname of Hercules; hence, Arx Monoeci, a promontory and harbor in Liguria, the mod. Monaco: portus Herculis Monoeci, Plin. 3, 5, 7, § 47; Tac. H. 3, 42: Arx Monoeci, Verg. A. 6, 830; Luc. 1, 408; Amm. 15, 10, 9.
Called also: Saxa Monoeci, Sil. 1, 586.