debelo

1. colloq. badly; heavily; way
   Ako misliš da ću ti oprostiti, debelo se varaš. — If you think I'll forgive you, you're badly mistaken.
   Taj stan su debelo preplatili. — They way overpaid for that flat.
2. thickly
   Debelo namaži hleb puterom. — Spread the butter thickly on the bread.

In the figurative sense it usually goes with verbs like varati se, zakasniti, platiti, zaraditi.