Polysynthesis is informally understood as the packing of a large number of morphemes into single words, as in (1) from Bininj Gun-wok (Evans, in press).
'I cooked the wrong meat for them again.'
Its status as a distinct typological category into which some of the world’s languages fall, on a par with isolating, agglutinating, or fusional languages, has been controversial from the start. Nevertheless, researchers working with these languages are seldom in doubt as to their status as distinct from these other morphological types. This has been complicated by the fact that the speakers of such languages are largely limited to hunter-gatherers—or were so in the not too distant past—so the temptation is to link the phenomenon directly to way of life. This proves to be oversimplified, although it is certainly true that languages qualifying as polysynthetic are almost everywhere spoken in peripheral regions and are on the decline in the modern world—few children are learning them today.
Perhaps the most pervasive of the traits that give these languages the impression of a “special” status is that of holophrasis, which can be defined as the (possible) expression of what in less synthetic languages would be whole sentences in single complex (usually verbal) words. It turns out, however, that there is much greater variety among polysynthetic languages than is generally thought: there are few other traits that they all share, although distinct subtypes can in fact be distinguished, notably the affixing as opposed to the incorporating type.
These languages have considerable importance for the investigation of the diachronic complexification of languages in general and of language acquisition by children, as well as for theories of language universals. The sociolinguistic factors behind their development have only recently begun to be studied in depth. All polysynthetic languages today are to some degree endangered (they are dying off at an alarming rate), and many have been poorly studied if at all, which makes their investigation before it is too late a prime goal for linguistics.