Why is Onigiri called so? and its literal Meaning
As I wrote in the previous post, Onigiri is a rice ball dish different from Nigiri. The latter is a style of sushi, but Onigiri is not.
Some might wonder why Onigiri is not the polite form of the word Nigiri, as the polite way to say Sushi is O-Sushi.
Why is it called Onigiri (おにぎり)?
Based on those sources, the etymology of Onigiri comes from the act of grasping rice, meaning ご飯を握る in Japanese.
In ancient Japan, rice was called 飯/いひ (Ihi), and 握飯/にぎりいい (Nigirii) was the word for Onigiri.
Later, the pronunciation Nigirii changed into Nigiri-Meshi (literally meaning grasped rice), and it is considered that Onigiri, as its feminine expression, came to be used.
Even now, we Japanese use Nigiri-Meshi as a synonym of Onigiri, and given the context above, the literal meaning of both is; grasped rice.