The verb 'to display' is ku-onyesha, the double causative of ku-ona. Hence the noun is maonyesho, with a 'y'.
It's JI/MA and yes, it only occurs in the plural, to my knowledge. The derivation is interesting: it's from the verb kuona (to see), then its causative form kuonesha or also kuonyesha (to "cause to be seen," or to show). Turn it into a noun by adding "ma-" and it literally means "showings."
Based on your explanation the word that came to mind was exhibition, and, sure enough, the hover hint gives "Exhibition/Display" as an alternative meaning.