aposiopesis

noun1

1. •
   (rhetoric) An abrupt breaking-off in speech, often indicated in print using an ellipsis (…) or an em dash (—).

   • —"My sister, mayhap," quoth my uncle Toby, "does not choose to let a man come so near her ****" Make this dash—'tis an Aposiopesis.—Take the dash away, and write Backside,—'tis Bawdy. — 1759