mukom

1. in dead silence; without a word
   Svi su mukom ćutali kad je ušao. — When he came in, everyone kept dead silent.
   Kad je saopštio vest, svi su mukom zamukli. — When he broke the news, everyone fell dead silent.
2. with great difficulty; through hard toil
   Sve što ima stekao je mukom. — Everything he has he earned through hard toil.
   Mukom zarađen novac se ne troši lako. — Hard-earned money is not spent lightly.

In the sense 'in silence' it is most often used with verbs like ćutati, zamuknuti, zanemeti; in the sense 'with effort' often with participles like stečen, zarađen.