Aposiopesis

Aposiopesis (/ˌæpəsaɪ.əˈpiːsɪs/; Classical Greek: ἀποσιώπησις, "becoming silent") is a figure of speech wherein a sentence is deliberately broken off and left unfinished, the ending to be supplied by the imagination, giving an impression of unwillingness or inability to continue. An example would be the threat "Get out, or else—!" This device often portrays its users as overcome with passion (fear, anger, excitement) or modesty. To mark the occurrence of aposiopesis with punctuation, an em dash (—) or an ellipsis (…) may be used.