Swing by a string, say Crossword Clue

 The answer to the crossword clue "Swing by a string, say" is DANGLE.

Dangle means to hang loosely and swing freely. It can also mean to suspend or hang something from a string.

For example, you might say that a pendulum dangles from the ceiling, or that a pair of earrings dangles from your ears.

The crossword clue is a clever way to clue the answer dangle, as it uses the image of a swinging object to evoke the meaning of the word.