to be nervous or worried

Don't fret - I'm sure he's OK. 别发愁——他肯定没事。

She spent the day fretting about/over what she'd said to Nicky. 她为对尼基说的话而担心了一整天。

any of the small raised metal bars across the long, thin part of a stringed musical instrument such as a guitar, that show you where to put your fingers on the strings in order to produce different notes