mrva

1. crumb
   Na stolu su ostale mrve od hleba. — There were bread crumbs left on the table.
   Ptice su pojele sve mrve. — The birds ate up all the crumbs.
2. a bit; a tiny amount
   Nema u njemu ni mrve stida. — He hasn't got a shred of shame.
   Sačekaj mrvu, odmah dolazim. — Wait a bit, I'm coming right away.

The phrase ni mrve (+ gen.) means "not a bit, not at all".