sirot

1. poor; unfortunate
   Siroti pas je ceo dan bio napolju na kiši. — The poor dog was outside in the rain all day.
   Sirota žena, ostala je bez posla pred penziju. — Poor woman, she lost her job just before retirement.
2. poor; needy
   Rođen je u sirotoj porodici na selu. — He was born into a poor family in the countryside.
3. dated orphaned
   Baka je podigla sirotu decu svoje ćerke. — Grandma raised her daughter's orphaned children.

For "lacking wealth" siromašan is more usual; sirot mostly expresses pity.