Merya or Meryanic is an extinct Finno-Ugric language, which was spoken by the Meryans. Merya began to be assimilated by East Slavs when their territory became incorporated into Kievan Rus' in the 10th century. However some Merya speakers might have even lived in the 18th century. There is also a theory that the word for "Moscow" originates from the Merya language. The Meryan language stretched to the western parts of Vologda Oblast and Moscow.
There is no general agreement on the relationship of Merya with its neighboring Uralic languages. It is sometimes left as unclassified within the western end of the family.
Rahkonen (2013) argues that the likewise unattested and unclassified-within-Uralic Muromian language was a close relative of Merya, perhaps even a dialect of Meryan.
A probable characteristic of the Merya language, which some researchers have noted, is the plural -k, while most Uralic languages use -t for the plural.
There have been attempts to re-construct Merya based on toponyms, onomastics and words in Russian dialects by O. B. Tkachenko, Arja Ahlqvist and A. K. Matveev among others. The first reconstructions were done in 1985 by O. B. Tkachenko. The latest book about Merya reconstructions was published in 2019. As an example: in Russian toponyms around where Merya was spoken, an ending -яхр (-jaxr) is regularly seen in names relating to lakes. This also resembles, but does not exactly match, the words for 'lake' in western Uralic languages, such as Finnish järvi, Northern Sami jávri, Erzya ерьке (jerʹke), Meadow Mari ер (jer) (from a common proto-form *jäwrä). From these it can be inferred that -яхр likely continues the Meryan word for 'lake', which may have had a shape such as jäkrä, jähr(e)
According to Rahkonen, in Merya areas there is a word veks, which is probably cognate with the Komi word вис (vis) 'middle river', and similar also to an element vieksi which appears in Finnish toponyms. From Merya toponyms it can also be seen that words such as volo 'down' (Finnish: ala), vondo 'give' (Finnish: antaa) existed in the Merya language. From this it can be concluded that Finnish a- corresponds to vo- or o- in the Merya language. Another thing that can be observed is the Finnish sound "a" corresponding to a Merya "o", for example a hydronym kol(o) can be seen, which can be compared to Finnish kala 'fish'. In the Muroma-Merya territory a word il(e) can be observed, which can be compared to Finnic *ülä ‘upper’.
Meryan phonology has been studied only in general terms, relying on Russian dialects in the Kostroma and Yaroslavl regions. Helimski suggests that Merya likely developed massive reduction of word-final syllables. The Merya language only allowed one consonant at the beginning of words, and likely placed stress on the first syllable of the word. It likely did not feature vowel harmony. The vowels /ö/, /ä/ and /y/ likely existed in the Merya language.