[Prob. a fanciful alteration of ROUNCIVAL.]
A nonsense word used by Edward Lear in runcible cat, hat, etc., and esp. in runcible spoon, in later use applied to a kind of fork used for pickles, etc., curved like a spoon and having three broad prongs of which one has a sharp edge.
The illustrations provided by Lear himself for his books of verse give no warrant for this later interpretation.
My wife, who was reciting The Owl and the Pussycat to our daughter, used this word the other day and I expressed some mild disbelief that it was a real word. Turns out, as you can see above, that it is; the word was concocted by Edward Lear and the first usage was in the aforementioned poem.