Non-Lingistic words are normally known as Interjections for they are both words AND parts of speech. Parts of speech are simply CLASSIFICATORY labels applied to words; for ex. words are either nouns, adjectives, verbs, prepositions, etc. So by definition, all words necessarily belong to a given part of speech. Interjections are probably the most "non linguistic" words since they usually have very little grammatical structure and very little true "semantic" meaning, the way nouns, adjectives, verbs or adverbs have. That is why linguists have not been very interested in them, since they can only be "listed".
Interjections are traditionally counted as one of the parts of speech, just like nouns and verbs. However, every word of English is considered a member of some part of speech, so that calling an interjection a word is also correct. The simplest way to classify them is by using the process of exclusion; when you have determined that a word is not one of any of the other parts of speech, it must be an interjection. There is of course the problem of drawing the line between an interjection and a _noise_. That is, when someone says "Ouch!" we recognize that as a word and classify it as an interjection; but there are many sounds a person might make in response to sudden pain that aren't recognized as words at all --- for example, there might be a sudden hiss caused by drawing the breath in sharply through closed teeth after someone had accidentally touched a hot stove. That hiss would not be either a word or an interjection. English adult speakers usually make the distinction along the following lines:
When he touched the hot stove he said, "Ouch!"
When he touched the hot stove he went "Sssssssssssssssss!"
More examples of non-linguistic words are:
tsk tsk
hee hee
ummmm
etc.
Usually the classification is semantic, ie, by what meaning they convey usually (eg, surprise, awe, pain, (dis)agreement, etc.)
I hope this answers your question.
Rev. Alimae
OP
