sprachbund
A group of languages sharing a number of areal features (similar grammar, vocabulary, etc.) which are primarily due to language contact rather than cognation.
[…] Certainly it is 'nicer' to define a sprachbund by what appear to be exclusively shared features with differentiate it from its neighbors – just as it is 'nicer' to be able to define a dialect by a set of innovations which clearly mark it off from other, related dialects. In the case of dialect continua, it has been known for a long time that this approach is unrealistic and historically inaccurate […]
Where it comes from
Borrowed from German Sprachbund (literally “language alliance, language association”), from Sprache (“language; way of speaking, speech”) (ultimately from Proto-West Germanic *sprāku (“language; speech”)) + Bund (“alliance”) (from binden (“to bind, to tie up”), ultimately from Proto-Indo-European *bʰendʰ- (“to bind”)). The German word was coined by Russian linguist Nikolai Trubetzkoy (1890–1938) in a paper he presented to the inaugural International Congress of Linguists in 1928 as a calque of the Russian term языково́й сою́з (jazykovój sojúz, literally “language union”), which he had introduced in a 1923 article.
Adapted from the Wiktionary entry sprachbund (CC BY-SA 4.0).