In Russian adjectives agree with the nouns they modify in gender/number and case. Out of 24 combinations only 12 forms are different. This system is completely regular, with no change of stress. The endings have “hard” and “soft” variants depending on the stem (for example, ый/ий or “ая/яя”).
Here is the Nominative and Genitive for “classic” hard- and soft-stem adjectives ("new"/"blue"):
NOM | GEN | |
---|---|---|
fem | но́вая/си́няя чашка | но́вой/си́ней ча̒шки |
masc | но́вый/си́ний дом | но́вого/си́него до́ма |
neut | но́вое/си́нее окно́ | но́вого/си́него окна |
pl. | но́вые/си́ние ча́шки | но́вых/си́них ча́шек |
note that masculine and neuter merge in all their forms different from the Nominative one (their Accusative will be the same as the Gen. or the Nom. depending on animacy). In the Nominative there is also -ОЙ masculine ending: большо́й (“big”). Only for ending-stressed adjectives.
The following universal rules of Russian spelling will give you the rest of the endings for any adjective you ever meet (there exist 4 patterns at most):