sladiti

1. (of food and drink) to sweeten
   Čaj uvek sladim medom, a ne šećerom. — I always sweeten my tea with honey, not sugar.
   Da li sladiš kafu? — Do you take sugar in your coffee?
2. (sladiti se + instr.) to relish; to savor
   Deca se slade kolačima koje je baka napravila. — The kids are enjoying the cakes Grandma made.
3. formal to sweeten; to make pleasant
   Muzika mu je sladila duge zimske večeri. — Music sweetened his long winter evenings.
4. derog. (sladiti se + instr.; of others' misfortune) to gloat; to revel in
   Sladi se tuđom nesrećom. — He gloats over other people's misfortune.

In everyday speech it is often used when asking whether someone takes sugar: Da li sladiš kafu?