prefix

in Japanese language we often feel certain some respect in word used prefix 'o'. for example food name, Osushi, Osashimi, Osoba. and there're some words we don't use the prefix "o", Tempura, Sukiyaki, Ramen. Vague/ambiguous is the usage 'o' to Sekihan, Udon. family member names, Otousan, Okaasan, Oniisan, Oneesan. Otouto, Imouto. If we eliminate the prefix 'O' , tousan'd have another meanings, too, 'touto' can't make sense. originally the word "Imouto" haven't the prefix 'O', if we use prefix 'O' to it she exudes an flavor of sweet potato.