aposiopesis

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aposiopesis
— from Classical Greek ἀποσιώπησις, “becoming silent”
— 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 (eg: “For 23 years, I’ve been dying to tell you what I thought of you, and now… well, being a Christian woman, I can’t say it!” – Auntie Em, The Wizard Of Oz)