I'm reopening this old thread to resolve a disagreement in the thread about the meaning of the word. (Aside - I just encountered the word this morning in a newspaper article reporting on a US court ruling stating that the plaintiff's argument was "vague and conclusory".)
The definition in #2 above is apparently incorrect in describing current legal usage in the U.S.; the definition in #4 is correct. I'll restate it, correcting two typos: "Expressing a factual inference without stating the underlying facts on which the inference is based."
There is another thread in Leo (Siehe auch: conclusory) which defines the word correctly and which offers the German unsubstantiierte Schlussfolgerung oder Behauptung.
(See the article cited in "Quellen", above, for a lengthy description of the historical use of the word.)
If anyone makes a dictionary entry, it should be flagged as "legal", "rare", and "U.S."
