The original Anglo-Saxon speakers preserved many words from the earlier Celtic languages, just as they almost certainly preserved words from still earlier languages whose names we don't know. Invasion, occupation and settlements gave us a huge shot of vocabulary from French and the Scandinavian languages, while the later rise of learning spawned numerous words derived from Latin and Greek.
In the past few centuries, English-speakers have conquered and colonised all over the world. Besides exporting English, we've also imported vocabulary from many of these places — India (eg bungalow, pyjamas), Australia (eg kangaroo, boomerang) and the Americas (eg potato, wigwam). And some words have just crept in randomly over the centuries, such as algebra from Arabic and robot from Czech.
Even in a ragbag language like English, some words have truly bizarre origins, and I thought I'd give a few examples.
It's such a simple word, but extremely versatile, used as adverb, preposition, adjective, noun and verb. It was originally a noun, though, and one of those words the Anglo-Saxons stole from the Celts. The word dun actually meant a hill, and it still survives in the plural as downs, especially referring to the chalk hills in southern England.
From this derived adune, literally meaning from the hill — in other words, towards a lower level. This is sometimes found in older or archaic language as adown, but it was soon shortened to its current form.
This was originally a preposition (He walked down the stairs) or an adverb (She put it down), but in modern English it can also be used as an adjective (He took the down escalator), a verb (The workers downed tools) or, coming full circle, a noun (She weathered the ups and downs of life). All from an ancient word for a hill.
The word item is actually Latin for also. Its modern English use came from an old system, often found in Shakespeare's plays, for instance, of making lists. A list would begin imprimis (firstly), and then each subsequent thing on the list would be preceded by item (also).
Over time, it became so common to write or reel off lists in this way that the word came to be seen as merely signifying the different "things" on the list. Since there was no word for this at the time, they came to be known as items, and the meaning has since extended so it can refer to any discrete object or concept that might be (but isn't necessarily) part of a list.
This is perhaps the strangest of all. The word check or words closely derived from it can mean to stop something, to make sure things are OK, a pattern of squares or a promissory note from a bank, and you'd be forgiven for assuming some of these, at least, are unrelated homophones.
In fact, every single meaning of the word derives ultimately from the Persian word for king, shah. This is normally pronounced in English without a final consonant, but I'd guess (I'm not a Persian speaker) the h should actually be sounded, giving something that could be distorted into check.
It was introduced to western Europe through chess. Several chess terms derive from Persian (the rook, for instance, is a chariot) and you call out check to indicate you're attacking your opponent's king (effectively look to your king). Checkmate means the king is dead.
As any chess-player knows, if you're put in check you have to suspend all your cunning plans to get out of check, so the word came to be used to mean stopping someone from completing what they're doing, such as checking an attack. From that, it turned into checking yourself — looking before you leap — and then to mean investigating that something was as it should be. Finally, in the US it's come to signify the mark known as a tick in the UK to show that something's been checked.
In the meantime, the word became attacked to the chess board, which became known as a checker or chequer board (the game of draughts, played on the same board, is known as checkers in the US). From this, any pattern of alternating-coloured squares came to be referred to as a check or checkered pattern, and this is used metaphorically now, such as talking about someone's checkered past.
The chequer board, though, wasn't only used to play games on. It was also the main form of abacus in mediaeval Europe, and its ubiquitous use led to any counting-house being referred to as an exchequer. This included the government's financial department, which is why the chief financial minister in the UK is called the Chancellor of the Exchequer. Banks, which were common in the Islamic world and brought to Europe by returning crusaders, had their exchequers too, and the promissory notes they issued were referred to as cheques. In the US, they're checks, and this can also refer to a bill for payment, especially in a restaurant.
So, whether you're making an inventory, wearing a gingham dress or writing a note to transfer money from your bank account — not to mention getting the upper hand at chess — you're actually invoking the Kings of Persia. Even if you don't know it.