najstarsza

In a sentence

• Najstarsza książka w bibliotece jest bardzo wartościowa.

  The oldest book in the library is very valuable.

  Here, 'najstarsza' modifies 'książka', meaning 'the oldest book', indicating possession of the quality of being old to the highest degree among comparable items.

• Moja najstarsza siostra właśnie skończyła studia.

  My oldest sister has just graduated from university.

  In this sentence, 'najstarsza' modifies 'siostra', meaning 'the oldest sister', referring to the sibling who is the most advanced in age relative to the others.

• Najstarsza góra w Polsce jest częścią Sudetów.

  The oldest mountain in Poland is part of the Sudetes.

  Here, 'najstarsza' refers to a mountain that is considered the oldest one in Poland, denoting a comparison based on age among mountains.