Polysynthetic languages

In linguistic typology, polysynthetic languages are highly synthetic languages, i.e. languages in which words are composed of many morphemes (word parts that have independent meaning but may or may not be able to stand alone). Polysynthetic languages typically have long "sentence-words" such as the Yupik word tuntussuqatarniksaitengqiggtuq which means "He had not yet said again that he was going to hunt reindeer." The word consists of the morphemes tuntu-ssur-qatar-ni-ksaite-ngqiggte-uq with the meanings, reindeer-hunt-future-say-negation-again-third.person.singular.indicative; and except for the morpheme tuntu "reindeer", none of the other morphemes can appear in isolation.

Whereas isolating languages have a low morpheme-to-word ratio, polysynthetic languages have a very high ratio. There is no generally agreed upon definition of polysynthesis. Generally polysynthetic languages have polypersonal agreement although some agglutinative languages that aren't polysynthetic can also have it, such as Basque, Hungarian and Georgian. Some authors apply the term polysynthetic to languages with high morpheme-to-word ratios, but others use it for languages that are highly head-marking, or those that frequently use noun incorporation.

Polysynthetic languages can be fusional or agglutinative depending on if they encode one or multiple grammatical categories per affix.

At the same time, the question of whether to call a particular language polysynthetic is complicated by the fact that morpheme and word boundaries are not always clear cut, and languages may be highly synthetic in one area but less synthetic in other areas (e.g., verbs and nouns in Southern Athabaskan languages or Inuit languages). Many polysynthetic languages display complex evidentiality and/or mirativity systems in their verbs.

...
Wikipedia