"Aposiopesis" is a new one for me. Stumbled across this one reading R.T. France on Mk 11.31-33 (in his NIGTC volume) this morning.

The four words that remain, ἀλλὰ εἴπωμεν ἐξ ἀνθρώπων, can be construed either as the beginning of a second conditional clause matching ἐὰν εἴπωμεν ἐξ οὐρανοῦ in v. 31, but with the ἐάν left unexpressed, or as a further deliberative question, ‘But shall we say “From men”?’, or even as a tentative decision on their part, ‘But let us say “From men” ’, which is then aborted by their recognition of the diplomatic gaffe that would involve. While the general sense is clear, the syntax is awkward, and the decision on how to punctuate the aposiopesis after ἀνθρώπων is a matter of taste.

France, R. T. (2002). The Gospel of Mark : A commentary on the Greek text (455). Grand Rapids, Mich.;  Carlisle: W.B. Eerdmans;  Paternoster Press.

Here's the definition from MW's eleventh edition:

"the leaving of a thought incomplete usu[ally] by a sudden breaking off (as in “his behavior was—but I blush to mention that”)

Merriam-Webster, I. (2003). Merriam-Webster's collegiate dictionary. Includes index. (Eleventh ed.). Springfield, Mass.: Merriam-Webster, Inc.

Here's the text; France is referring to the spot in v. 32, at the end of the words attributed to the scribes and chief priests (where the ESV has an emdash).

31 And they discussed it with one another, saying, “If we say, ‘From heaven,’ he will say, ‘Why then did you not believe him?’ 32 But shall we say, ‘From man’?”—they were afraid of the people, for they all held that John really was a prophet. 33 So they answered Jesus, “We do not know.” And Jesus said to them, “Neither will I tell you by what authority I do these things.” (Mk 11.31-33)

Update (2008-05-26): Two excellent comments on this post. The first, from David Fish, is a pointer to a blog post of his own where he recollects his first experience with aposiopesis. Do check it out, and check out David's blog, Random Thoughts from a Fish, as well. 

The second is a comment from Dave Novick, reminding us to check Bullinger's Figures of Speech for these sorts of things. Dave writes, "He's got an article devoted to it on page 151. The article divides the good number of Biblical examples into 4 categories: Promise, Anger and Threating, Grief and Complaint, Enquiry and Deprecation. I thought I'd pass that on, in case you (and others) weren't already familiar with it."

So there you go.