a comparison: a saying or story that teaches by setting one thing beside another, from a one-line proverb to a full narrative
At its root this word means a placing side by side, so its core idea is comparison: it sets a familiar scene next to a deeper truth and lets the likeness do the teaching. In the first three Gospels it is the standard label for the way Jesus taught, and it covers far more ground than the modern English "parable" suggests.
What holds the whole range together is not a fixed length or form but the move of comparison itself. A single arresting line ("physician, heal yourself"), a brief picture (the mustard seed, the leaven), and an extended story (the prodigal son, the wicked tenants) are all called by this one word, because each works the same way: it draws the hearer from the everyday picture to the point it illustrates.
The breadth comes from the Hebrew background. The Greek Old Testament used this word to translate a Hebrew term (משׁל) that already stretched across proverb, taunt, oracle, riddle, and allegory, and that elastic range was carried straight into the Gospels. So the word can lean toward a pithy proverb at one edge and toward a veiled, riddle-like saying at the other, while its center stays the illustrative comparison.
A comparison of this kind also asks something of the hearer. It does not hand over its meaning flat; it invites the listener to do the work of carrying the picture across to the truth, which is why the same teaching can open up to one person and stay closed to another.