Learn Polish: Śmierć jest końcem życia.

In Polish, when you use the verb być (to be) to state that one noun is another noun, the second noun must be in the Instrumental case. Because death is the end, the word for the end takes the Instrumental form.

How did koniec turn into końcem? Where did the letter e go?

This is a great example of the mobile e in Polish. When adding endings to certain words, the last e in the dictionary form disappears. When that e drops from koniec, the n also softens into ń before the -em ending, giving us końcem.

Why is the word for life written as życia instead of życie?

It is in the Genitive case, which is frequently used to show connection or belonging, functioning exactly like the English word 'of'. Because of this, końcem życia translates perfectly to 'the end of life'.

The word śmierć (death) ends in a consonant. Does that mean it is a masculine noun?

No, śmierć is actually a feminine noun. While most feminine nouns end in -a, there is an important group of feminine nouns that end in a soft consonant. Other common examples you might already know are noc (night) and rzecz (thing).