What's the origin of "brand-new"?
What is the origin of the expression "brand-new"? Anything to do with brand names?
Sort of. Our modern term "brand" comes from the idea of branding cattle with a distinctive ID mark. The word is related to the Old English baernan, to burn. "Brand-new" goes back to the Middle Ages, when it referred to pottery or metalwork that had just been pulled from the fire in which it had been hardened. A similar term was span-nyr, "chip-new," referring to the fresh-cut chips made by an axe. That's why you sometimes hear "brand spanking new."
Love letters from the Teeming Millions
You get "B" on "brand-new," "F" on "spanking-new." Although it's true that a newly-marked calf is literally "brand-new," it was even earlier that wine bottle corks were "branded" with a manufacturer's mark. As for "spanking-new," you must be wet behind the ears yourself, else you'd know the expression reflects the slap administered by a midwife or other assistant at the birth of a child to provoke crying, hence breathing.
That's very imaginative, J. — I like it when the Teeming Millions show a little creativity — but it's wholly unsupported by authority, unless of course you contend that as an "etymologist" you're the authority, in which case I'd like to see a little ID. My source on "spanking new" was Horsefeathers and Other Curious Words (1958) by the late dictionary editor Charles Funk and his son Charles Junior.
Moving on to other sources, we find that the Oxford English Dictionary lists several derivatives of span-nyr, such as "span-new," "spanker-new," and "spank span-new." It seems reasonable, therefore, to conclude that "spanking new" is more of the same. Then again, the OED also lists "spanking," possibly derived from the Danish spanke, "to strut," which means big, fine, vigorous, etc. One might make the case that this is the source of "spanking new." William and Mary Morris, authors of the Morris Dictionary of Word and Phrase Origins, claim "spanking" comes from a Scandinavian sailor's term used to describe a fresh, lively breeze. One can see how this might reasonably be coupled to the concept of newness in "spanking new." Be that as it may, nobody says anything about spanking babies.