String tightener on a guitar

PEG

Think of the wooden knob at the end of the guitar’s headstock that you turn to adjust pitch—it’s not the tuning key on modern guitars.

A guitar peg is the small knob at the end of the neck that you turn to tighten or loosen the strings, adjusting their pitch. The clue plays it straight—no wordplay or tricks—just a direct reference to the part that holds the strings in place. If you’ve ever tuned a guitar, you’ve twisted these pegs to get the right sound. Some people also call them tuning pegs or machine heads, but "peg" fits neatly in crosswords.