struna

1. (of an instrument) string
   Pukla mu je struna na gitari. — A string on his guitar broke.
   Violina ima četiri strune. — The violin has four strings.
2. (in fishing) fishing line
   Riba je pokidala strunu. — The fish snapped the line.
   Kupio je novu strunu za štap. — He bought new line for his rod.

In everyday speech guitar strings are more often called žice.