Scale, as in "to climb up" comes from the Latin scala, meaning "ladder". A musical scale is probably derived from this definition, because the notes go up and down.
Scale, as in "a moveable plate on the skin of a fish or lizard" comes from the Old French escale, meaning "shell or husk".
And scale as in "measuring device" comes from the Old Norse skal, a drinking cup sometimes used as measuring device.
That Old French escale ultimately comes from the Frankish word skala, which has a similar meaning to the Old Norse skal, and most French is derived from Latin, which means that the Latin scala is likely an influence in either or both of those words as well, so what we have here is a big old chicken-and-egg problem of linguistic origin.
The upshot of all this is that we have four (and more) words in modern English with exactly the same spelling and pronunciation, but completely different meanings.
The fancy word for this is homonym, meaning "same name".
The sheer scale of absurdity (do you see what I did there? Huh? Huh?) within English is magnified when you look at words like cough, thought, through, and drought - each with a different pronunciation - or words like knight and knife, with a silent letter for seemingly no reason.
Well... in truth, those -ough words all most likely used to rhyme. And the Ks in knight and knife were originally pronounced - actually, all the letters in knight were, giving us something that sounded like "k-NEE-gt". So what the heck happened there?
Well, in the Middle Ages, English underwent something called the "Great Vowel Shift", where the pronunciations of a lot of words changed very drastically under a relatively short period of time. Language is a living and flexible thing, so this isn't unusual of itself, but the timing was very strange, since the printing press had very recently been invented, so English had, for the first time in its history, had the spellings of most words standardized, meaning that they were to be spelled the same way by every writer (I suppose before that it was sort of a free-for-all, figure-it-out-yourself kinda thing).
So it's not so much that English is a strange language with a bunch of arbitrary, made-up rules about pronunciation, so much as our writing system was standardized for a pronunciation of English that nobody speaks anymore. I bet that if the Great Vowel Shift had happened about a century earlier, our spelling would look much, much different - knight and night could both be spelled nite, for example, and your doctor would say that you ott to bie some coff syrup when you're going thrue a cold.
So the next time you're tempted to say, "English doesn't make any sense!", bear in mind that it does - you just need to have a good head for history to understand it. And if all else fails, just pretend that what you speak and what you read are two different languages - because they sort of are!
