Open class words belong to a list of morphemes which can be added to by absorbing new words, such as technical terms, slang, as well as adoptions and adaptations of foreign words.

The list of groups of words that belong to the open class type include:

Interjections particularly, are formed as new words standing in for sounds, and are added not only from technical backgrounds, but also from sources such as comicss and subtitling. It is in these that one will encounter the noises of motor revving, sirens, mechanical sounds and violence, continuously being updated. Examples here are: vroom!, va-va-voom!, zonk!, grrh!, and so on.

Closed-class words such as prepositions, conjunctions, pronouns, etc., are words belonging to a class to which no new words can be added readily.