The article is devoted to the comparison of semantic development of Protoslavonic base *t'ud' in Czech, Russian and Slovene languages. It is known that in Protoslavonic period the word *t'ud' denoted "national", the meaning gradually changed up to the onomatopoeic one.
We can't state, that the modern meanings of adjectives cizí, čužoj and tuj are synonymous: the meaning in Russian doesn't imply submeaning "foreign", Slovene still has the meaning "national" in one of its dialects. We are going to take a look not only at today's meanings, but at the dynamics of semantic development from the Old Slavonic period up to modern languages, and will find out how was the meaning and word configuration changing in the above-mentioned languages.