брат

In a sentence

• Мой брат любит играть в шахматы.

  My brother likes to play chess.

  Here, 'брат' is used to mean a sibling, specifically a male one, referring to a family relationship commonly used in introduction contexts.

• Привет, брат, как дела?

  Hi, brother, how are you?

  In this instance, 'брат' is used colloquially and informally as a friendly term, not necessarily indicating a familial relationship, similar to 'bro' in English.

• На войне он потерял многих боевых братьев.

  In war, he lost many of his battle brothers.

  'Братьев' here stems from 'брат' and is employed metaphorically to denote close comrades or companions, often used in military or fraternal contexts.