oslabeti

1. (of a person, strength, senses) to weaken; to grow weak
   Posle bolesti je jako oslabeo. — He grew very weak after his illness.
   Vid mi je oslabeo poslednjih godina. — My eyesight has weakened in recent years.
2. colloq. (of body weight) to lose weight
   Oslabela si, baš ti lepo stoji! — You've lost weight, it really suits you!
   Oslabeo je deset kila za dva meseca. — He lost ten kilos in two months.

In everyday speech in Serbia the forms of oslabiti (oslabio, oslabila, oslabiću) are more frequent in these meanings, but the forms of oslabeti (oslabeo, oslabela) also occur in ordinary usage. The imperfective is slabiti; in the sense 'lose weight' the amount often follows: oslabiti pet kila.