My local Irishman here at work mentioned how he’d used the phrase “to boot” in an e-mail (as in “he took the wife and the kids, to boot”) and wondered whether any of the American recipients would understand it.
I assured him that we would, and that “to boot” was universally recognized from sea to shining sea, and then we go to speculating on where that phrase came from.
We came up blank (heck, we’re engineers, not linguists); do any Dopers know where this phrase comes from?
I searched for to boot on www.m-w.com and found a definition for boot that included that phrase. The etymolody given was
One of the meanings given was
Based on this, I would gather that the eytmology of that saying would be along these lines:
From that, I would expect the meaning generalized out to become “in addition,” losing the “to make better” connotation.
I’m sure somebody with ready access to an OED will be along shortly to make me sound like an idiot, though. 
This is, of course, the origin of a tune. :rolleyes:
Entomology? You mean like squashing bugs with your boot, until they’re completely dead?
{Just kidding}
The etymology of boot in the sense of ‘profit; use’: it’s an archaism that survives in the phrase to boot meaning ‘in addition, besides’, which appeared in Old English before 1000.
The old use of boot, Middle English bote ‘relief, remedy’ (1131, in the Peterborough Chronicle), developed from Old English bot ‘expiation for a crime or sin, compensation, remedy’; literally, ‘making better’ (about 725, in Beowulf). The Old English is cognate with Old Frisian bote ‘compensation, atonement’, Old High German buoz, buoza ‘improvement, remedy’, Old Icelandic bot ‘remedy, compensation’, and Gothic bota ‘advantage, benefit, good’, the from Proto-Germanic root of Old English bet and betera, ‘better’.
The unrelated word boot meaning ‘large shoe’ comes from Old French bote.
“Boot” is a verb meaning “to profit”. You could say, “It boots nothing to complain.” Meaning, “Complaining doesn’t get you anything.”
So if you say, “I’ll give you a cow, and a milking pail to boot!” you’re saying that you will give the person a cow, and add a pail to his profit. I think that this extra “profit” on a trade came to mean “in addition to” or “as well”.
So “to boot” is lagniappe.