vaga

1. scales; scale
   Stani na vagu da vidimo koliko imaš kila. — Step on the scale so we can see how much you weigh.
   Prodavačica je stavila paradajz na vagu. — The saleswoman put the tomatoes on the scales.
2. (zodiac sign) Libra
   Moja sestra je vaga, rođena je u oktobru. — My sister is a Libra, she was born in October.

Unlike Russian «весы», vaga is a singular noun.