Moreover, in addition to, as well as, besides, to advantage, into the bargain. It has nothing to do with footwear or feet. It’s entirely unrelated to the more recent English word ‘boot,’ the one that may give you blisters. But it is kin to the English words ‘better’ and ‘best.’
According to the Oxford English Dictionary, the original ‘boot’ is a very old noun that was used in Anglo-Saxon times to mean ‘advantage,’ ‘good,’ ‘profit,’ or ‘remedy.’ Those meanings are dead, for the most part. ‘Boot’ appears in many Old English manuscripts and may date from as far back as the early 700s. But its ultimate source is older than written language.
The earliest citation in the OED for ‘to boot’ (spelled ‘to bote’) is from Daniel, an anonymous and undated Old English poem inspired by the biblical Book of Daniel.
The word is used alone (as ‘bote’) to mean a medicinal cure or remedy in the Old English poem Elene, written by Cynewulf sometime between 750 and the late 800s, according to the OED.
It also appears (as ‘bot’) in Beowulf, which may date from 725, in the sense of compensation paid for injury or wrongdoing.
More modern appearances occur (as ‘to boot’) in Falk, by Joseph Conrad: “At all events he was a Scandinavian of some sort, and a bloated monopolist to boot,” and in Shakespeare’s play Antony and Cleopatra: “Give him no breath, but now / Make boot of his distraction” — in other words, take advantage of his being distracted.
Now for the other ‘boot,’ the one that’s made for walking. This ‘boot’ dates from the early 14th century, when it was borrowed from Old French (bote) and meant a sort of shoe, usually of leather, extending above the ankle.
The related sense of ‘boot,’ meaning the trunk of a car in British English, goes back a lot longer than you might think. According to the OED, since around 1608, ‘boot’ has been used to mean part of a horse-drawn coach. And since 1781 it’s meant a place to store luggage and cargo.
The word ‘bootstrap’ comes from the 19th-century, meaning a strap for pulling a boot on. But it was co-opted in the early 1950s by the computing industry to mean a fixed sequence of instructions that would initiate the loading of an operating system.
The term was first recorded, according to OED citations, in 1953 in Proceedings of the Institute of Radio Engineers:
“A technique sometimes called the ‘bootstrap technique.’ Pushing the load button … causes one full word to be loaded into a memory address previously set up … after which the program control is directed to that memory address and the computer starts automatically.”
In the 1970s and 1980s the word was shortened to ‘boot’ (both noun and verb), and today it’s used in most houses that have computers.
It’s also used in that same sense for other tasks, such as “I’m going to boot that engine into life.” I’m quite accustomed to this usage. But I will admit, on those rare occasions when my Mac and I get into a disagreement, I’d just as soon put the boots to it.