A part of speech in Japanese grammar, similar to English interjections. Often contrasted with 感動詞 (かんどうし), which is a broader or slightly different category in some grammatical traditions.
See also: 感動詞
"Aa" and "oya" are classified as interjections.
Compound of 間 (かん, 'interval') + 投 (とう, 'throw') + 詞 (し, 'word'), literally 'thrown-in word'. The term was coined in Japanese linguistics to translate the Western grammatical concept of interjection.