Okay little one, so a runcible is actually not a very common word that we use every day. It's a made-up word that was created by a writer named Edward Lear in a poem called "The Owl and the Pussycat". In the poem, the owl and the pussycat are getting married and they have a "runcible spoon" that they use to eat with.
Now, a runcible spoon looks kind of like a regular spoon, but it's a little different. It has a curved handle and instead of a traditional round-shaped scoop for the food, it has kind of a triangle shape with curved edges. Some people also use the word "runcible" to describe other objects, like a knife or a fork, that have a similar shape to a runcible spoon.
So, essentially, a runcible is a made-up word that refers to a spoon or utensil that has a unique shape with curved edges. It's not something you'll likely see or hear about in everyday conversation, but it's a fun word to know and use if you ever come across it!