Old Curonian disappeared in the course of the 16th century, leaving substrata in western dialects of the Latvian and Lithuanian, namely the Samogitian dialect. No written documents in this language are known, but some ancient Lithuanian texts from western regions show some Curonian influence.
Historian Marika Mägi proposes that Curonian was not originally seen as ethnic, but social category, depicting Eastern Baltic seafarers, who often engaged in piracy. She believes that early meaning of the name also included Finnic tribes living in northern Curonia and Saaremaa (historical parallel name of latter has been Kuresaar, "Kure-island"). Marika Mägi sees origin of the Curonian name in Finnic word kura (kuri, kure), meaning "something bad, despiteful, angry".
Linguist Eduard Vääri Curonians argues that it is possible that Curonians were Baltic Finns. Amateur historian Edgar V. Saks has pointed out several Curonian words and names of possible Finnic origin. For example, a treaty from 1230 calls Curonian administrative divisions kiligunden (kihelkond in Estonian) and the Curonian army maleva. The elder who signed the treaty was named Lammechinus (resp. Lemminkäinen). Self-denomination of Curonians, kure, according to Saks, means 'crane' in Estonian. The attested local Finnic language, Livonian, may be the source of Finnic elements in Curonian.