I know this is probably an incredibly dumb question but I was asked this the other day and didn’t have an answer other than, “It probably has to do with the etymology.” The question was why do we call it an oak tree but we call the seed an acorn?
I looked up the etymology of acorn and it said: Middle English akern, from Old English æcern; akin to
Old English æcer field, Middle High German ackeran acorns
collectively, Old Irish áirne sloe, Lithuanian uoga berry
Date: before 12th century.
Then I looked up the etymology of oak and got: Middle English ook, from Old English Ac; akin to Old High German eih oak and perhaps to Greek aigilOps, a kind of oak
Date: before 12th century.
My answer I thought I would obtain didn’t appear. They both seem to have a fairly close origin. So why do we call the tree an oak and the nut an acorn?
I haven’t been able to find much more info than what you already have. The OED basically confirms your emtymology. One interesting quote from the OED about acorn:
Apparently, acorn was once spelled ake-corn (i.e. oak-corn, where corn means a generic grain). This does not indicate the true relationship of the words. But the OED doesn’t explain what the real relationship between the words is. There may or may not be a connection between acorn and acre. WAG, there’s likely a some forgotten ancestral root of the three words. But who knows, the answer is probably lost.
According to the etymologies in the American Heritage Dictionary of the English Language, oak and acorn haven’t had anything to do with each other since at least Proto-Germanic. The etymology of acorn is given as “Middle English, variant of akern, from Old English æcern. See og- in appendix.” From the appendix we learn that og- is an Indo-European root with the basic meaning of fruit or berry; from there we get “zero-grade form *eg- [NOTE: that “e” is actually supposed to be an upside-down “e” or schwa sign, but if there’s a way to post a schwa on the Internet short of using a GIF file I’d love to know what it is–MEB] in Germanic *ak-ran- in Old English æcern, acorn”. Og- is also the root of the word “uvula”, of all things: in Latin, it wound up being the word for “grape”, and I guess some anatomist thought that the little dangly thing in the back of your throat looks like a little grape. The etymology of “oak” is “Middle English ok, ook, Old English ac, from Germanic aik- (unattested).” So, apparently they can’t trace oak all the way back to Indo-European, but they don’t think it has anything to do with og-. By the way, there should really be a couple more diacritical marks in there–that og- should have a straight line over the “o”, and so should the “a” in the Old English ac–but at this point I say the hell with them.
About all I can add to this extremely (if I do say so myself) fascinating topic is that “Oak” definitely doesn’t come from the Latin…
That and the not especially relevant thought that having a separate word for acorn may be and indication that acorns were fairly important to early English speakers. My understanding is that they were food source for fattening pigs, and based on this perhaps a very important one.