They dined on mince and slices of quince,
which they ate with a runcible spoon.
Another mention of this piece of cutlery appears in the alphabetical illustrations Twenty-Six Nonsense Rhymes and Pictures. Its entry for "D" reads
The Dolomphious Duck,
who caught Spotted Frogs for her dinner
with a Runcible Spoon
Lear does not appear to have had any firm idea of what the word "runcible" means. His whimsical nonsense verse celebrates words primarily for their sound, and a specific definition is not needed to appreciate his work. However, since the 1920s (several decades after Lear's death), modern dictionaries have generally defined a runcible spoon to be a fork with three prongs, such as a pickle fork, which is curved like a spoon, and also has a cutting edge. It should be noted that this definition is not consistent with Lear's drawing of a "runcible spoon", mentioned above, nor does it account for the other "runcible" objects in Lear's poems.
* Scroobious is an adjective which he applied to people in some of his verses, including the unfinished "Scroobious Pip." It seems to imply disapproval of their conduct, although the Pip is "the wisest" of whatever sort of beast he may be. It may be a pseudo-Latin derivative of screwball. The word has since been used by other people.
Which is your favorite word: Runcible, Scroobius or Spork?