Czechoslovakia (n.)

"member of the westernmost branch of the Slavic people," the native name for Bohemians (and including the Moravians), 1848, from Czech český "Bohemian, Czech," which is said to be from the name of an ancestral chief (who is mentioned in English by 1837). Room says "some" derive it from a source akin to Czech četa "army." Meaning "the Czech language" and use as an adjective both are also from 1848. Sometimes in early use, Tshekh, from French.

1829 (n.), "member of a Slavic race living mostly in the Carpathians, north of Hungary and east of Moravia; 1887 as an adjective, from French Slovak, from the people's own self-designation(compare Slovak and Czech Slovak, plural Slovaci; Polish Słowak; Russian Slovak; German Slowake). Related: Slovakian; Slovakish.