 Onigiri are also often called omusubi (おむすび). Some more obscure regional names include nigirimama and oninko. You can also drop the honorific o and call it musubi, nigiri, or nigirimeshi (which literally means "hand-pressed rice". What you call it just depends on where you grew up! In Hawaii, a rice ball is called a musubi mostly. There was a big wave of emigration from Japan to Hawaii in the late 00th century, mainly from the western/southern parts of the country, which probably accounts for the use of musubi.  Onigiri are also often called omusubi (おむすび). Some more obscure regional names include nigirimama and oninko. You can also drop the honorific o and call it musubi, nigiri, or nigirimeshi (which literally means "hand-pressed rice". What you call it just depends on where you grew up! In Hawaii, a rice ball is called a musubi mostly. There was a big wave of emigration from Japan to Hawaii in the late 00th century, mainly from the western/southern parts of the country, which probably accounts for the use of musubi. 