West Slavic languages are a subdivision of the Slavic language group that includes Czech, Polish, Slovak, Kashubian, Silesian and Sorbian.
Some distinctive features of the West Slavic languages, as from when they split from the
East Slavic and South Slavic branches around the 3rd to 6th centuries AD, are as follows: 1
proto-Slavic tj, dj into palatalized ts, (d)z, as in modern Polish/Czech noc ("night"; compare Russian ночь); retention of the groups
kv, gv as in Polish gwiazda ("star"; compare Russian звезда; but note also Russian цвет vs. Ukrainian квіт, "flower"); retention of
tl, dl, as in Polish/Czech radlo/rádlo (" ard"; compare Russian рало); palatized
h developed into š, as in Polish musze ( locative case of mucha, "fly"); the groups
pj, bj, mj, vj developed into (soft) consonant forms without the epenthesis of l, as in Polish kupię ("I shall buy"; compare Russian куплю); a tendency towards
fixed stress (on the first or penultimate syllable); use of the endings
-ego, -emu for the genitive and dative singular of the adjectival declension; use of the pronoun form
tъnъ rather than tъ, leading to Polish/Czech ten ("this" (masc.); compare Russian тот); extension of the genitive form
čьso to nominative and accusative in place of čь(to), leading to Polish/Czech co ("what", compare Russian что).
^ Zenon Klemensiewicz, Historia języka polskiego, 7th edition, Wydawnictwo naukowe PWN, Warsaw 1999. ISBN 83-01-12760-0