What’s the difference between a mickle and a muckle? That’s a trick question, obviously, because they both mean the same thing: they refer to something large, or large amounts of something.
But for non-Scots, these playful, almost child-like words were thought to be opposites of each other - and it arose from an old adage that itself was wrong from the outset.
“Mony a mickle maks a muckle” was widely understood to mean something along the lines of “many little things add up to a lot”. The correct expression should be “Mony a pickle maks a muckle”, but it is feasible that pickle was substituted for the sake of a more alliterative phrase.
Pickle/puckle, of course, means the opposite of mickle/muckle, ie. a little of something.
George Washington famously referred to the phrase in 1793, further obscuring mickle’s true meaning.
In most cases, muckle is used as an adjective: a muckle house, a muckle spoon, a muckle bucket and so on. Don’t be too liberal with it, though: you won’t win Charmer of the Year for referring to someone’s muckle waistline.
Langholm in Dumfriesshire has gone some way to putting the word back on the map, though - it is known colloquially as the Muckle Toon.