About 5,000 unaffixed stems have been reconstructed for Proto-Austronesian, Proto-Malayo-Polynesian, or Proto-Western-Malayo-Polynesian. Although the Indo-European languages have a far richer textual tradition, probably no language family excels Austronesian in the richness of vocabulary reconstructed through the comparative method.

The vocabulary of a language reflects the collective experience of its speakers, making reference to both their natural world and their culture. The reconstruction of vocabulary and the identification of loanwords thus can provide insight into the natural environment and culture of prehistoric language communities and the nature of their linguistic contacts.

Reconstructed vocabulary shows clearly that the speakers of Proto-Austronesian had grain crops, including rice and millet; that they lived in settled villages of houses raised on piles; that they practiced weaving on simple back looms; that they domesticated dogs, pigs, and probably chickens; and that they were in contact with the sea and its resources. Familiarity with many tropical food plants can be inferred for speakers of Proto-Malayo-Polynesian. These include the coconut, banana, yam, sugarcane, pandanus, taro, sago, and breadfruit. Of these only sugarcane, pandanus, and wild taros of the genus Alocasia can safely be inferred for Proto-Austronesian, which probably was spoken on both sides of the Tropic of Cancer.

Reconstructions for ‘boat,’ ‘sail,’ and ‘paddle’ can be attributed to Proto-Austronesian, but terminology specific to the outrigger can be assigned only to Proto-Malayo-Polynesian, a language that was probably spoken somewhere in the northern Philippines in the period 3500–3000 bce.

Lexicostatistics, a controversial method for studying word replacement in relation to subgrouping, often distinguishes a subset of terms called “basic vocabulary.” Lists of basic vocabulary words typically include those for body parts, terms for everyday natural phenomena (sky, wind, rain, sun, star, earth, stone, water, tree), basic kin terms (father, mother, child), and some others. Although lexicostatistical theory assumes a universally constant rate for the replacement of basic vocabulary, replacement rates in Austronesian languages appear to show considerable variation. Malay and its closest relatives (Iban, Minangkabau, and so on), many Philippine languages, and some languages in eastern Indonesia (Manggarai of the Lesser Sundas, Yamdena of the southern Moluccas) show very high concentrations of vocabulary items that have a wide distribution in the Austronesian family. It is inferred from this that they have replaced basic vocabulary at a slower rate than other languages. By contrast, languages in the South Halmahera–West New Guinea group and many of the Austronesian languages of western Melanesia show far lower concentrations of widely distributed forms, and it is inferred that they have experienced more rapid rates of basic vocabulary replacement. Some Oceanic languages—including several in the southeastern Solomons, Fijian, Polynesian (especially Samoan and Tongan), and the Chuukic (Trukic) languages of Micronesia—also have relatively large concentrations of widely distributed forms and have for this reason traditionally been highly valued as witnesses in comparative linguistics.