sem

In a sentence

• Eu fui à feira sem levar sacolas.

  I went to the market without bringing bags.

  The word 'sem' is used here to indicate the absence of 'bringing bags' while going to the market.

• Eles passaram o dia todo sem comer.

  They spent the whole day without eating.

  Here, 'sem' denotes the absence of 'eating' during the whole day.

• Não posso sair sem meu telefone.

  I can't go out without my phone.

  In this case, 'sem' signifies the absence or lack of 'my phone' as a condition for going out.