Learn Hardcore Russian: Учебник — источник новых слов.

In Russian, the dash often replaces the present form of the verb быть (“to be”) in simple declarative sentences. So Учебник — источник новых слов literally means “The textbook is a source of new words,” but the verb есть (or быть) is omitted and its place marked by a dash.

Why are Учебник and источник both in the nominative case?

In a nominal sentence (one without an explicit linking verb), both the subject and the predicate noun appear in the nominative. Here Учебник is the subject and источник is the predicate nominative, so both take nominative singular forms.

Why is новых слов in the genitive plural instead of the nominative?

In Russian, nouns like источник (“source”), контейнер (“container”), or words indicating “fullness” or “quantity” typically govern the genitive to show “of something.” Thus источник новых слов means “source of new words,” and новых слов is genitive plural.

How do you form the genitive plural for новое слово?

The noun слово is neuter. Its forms are: • Nominative plural: слова
• Genitive plural: слов (the -а drops)
The adjective новый in genitive plural becomes новых (ending -ых for hard-stem adjectives). Together: новых слов.

Can you express the same idea using a full verb instead of the dash?

Yes. For example:
Учебник является источником новых слов.
Here является (“is”) is the explicit verb, and источником is in the instrumental case because predicates with являться take the instrumental.

Why does источник change to источником with является? Shouldn't it stay nominative?

With the verb являться, Russian requires the predicate noun to be in the instrumental case, not nominative. So источник (nom.) becomes источником (instr.) to agree with является.

Is it acceptable to invert the order and say Источник новых слов — учебник?

Yes. Russian word order is flexible. Источник новых слов — учебник still means “A textbook is a source of new words,” but it emphasizes источник (“source”) first.

Where are the word stresses in Учебник — источник новых слов?

• Учебник: second syllable, Учеби́к
• источник: first syllable, Источник
• новых: first syllable, Но́вых
• слов: single syllable, слов