I suppose I should start out by saying that decimate has a very precise definition: to reduce by 10%. I’m not sure I have ever actually used the word except to talk about the word. I also just realized how wildly I would use a word that means to reduce to 10%. (1) Is there such a word? (2) If not, could we make one up? (3/4) What about a word that means to reduce by/to 1/2? Is (3) Bimate?
Edit: fixed the placement of (1) before the first reply.
Had a very precise definition. That definition has changed/evolved. Go ahead and look it up; even the dictionary acknowledges as much.
The word decimate is an English word. It has Latin roots but here’s the thing you must always remember: the original meaning of the roots of a word count for nothing when modern definitions are created. That means that English speakers and writers get to decide what decimate’s meaning is. They started using it to mean a large decrease in - and by extension 1/10 - as long ago as the 17th century. Anybody who doesn’t understand this or disputes this doesn’t understand how the English language properly works.
There is also a word mean to cut in half. It is halve. That’s been around since at least 1300.
Thank god I wasn’t the only one. This is almost verbatim what I came in to say.
How about “bisect” and “split”? Related for other fractions would be “trisect” and “quarter”, and I’m sure there are many more such.
Most definitely. And it would probably be cromulently understandable. However, making it a common enough word for dictionary editors to include it is an entirely different matter.
“Is there a word like decimate for an order of magnitude reduction?”
Yes. It’s “decimate,” in the original sense of the word.
An order of magnitude reduction, in base 10, **is **a reduction by 10%. 100,000 is one order of magnitude smaller than 1,000,000, for example.
I don’t see how does that helps me answer the related questions. If you can see how you from half to anything related then you should probably explain it.
Thanks for ignoring the thread hijackers and making an honest attempt! I take it you are suggesting decisect as an answer to (1)? Nifty word but I kind of feel like N-sect turns a single thing into a collection of N things. For example, if you bisect a cake you are left with two pieces of cake. Do you still think it works?
I think you win for best oxymoron of the day!
And you’re correct. My pet peeve, though, is when people are writing about Roman times and then use decimate in its modern meaning. I suppose it’s still technically correct, but if someone says “the Roman army was decimated” I really think they ought to have the Roman definition of the word in mind.
How sad. I use it frequently in describing a complete lopsided victory in sports.
Take ten pennies and reduce that collection by 10% and you have 9 pennies left. Reduction means subtraction: So 100% - 10% = 90%.
By that definition, a 2-orders of magnitude reduction would be a 1% reduction, and 3 orders of magnitude reduction would be a 0.1% reduction?? I don’t think so…
I was taught that “order of magnitude” referred to the exponent in a scientific notation … um … formula.
So, 1,000,000 (1x10[sup]6[/sup]) reduced by one order of magnitude would be 1x10[sup]5[/sup] or 100,000. Is that not right?
So I might have dismissed “half” too quickly. A tenth clearly has the meaning I am looking for in (1). If nobody else can come up with anything better then I just have to start getting you people to allow it as a verb.
‘Halve’ works as an order of magnitude in binary, so if you’re writing on a computer, just use that.
I’m not sure what there is to explain. The equivalent of decimate for “reduce to 1/10” is halve for “reduce to 1/2”. There are many other words for the act of cutting in half, but none are as precisely equivalent and none of them end in -mate. The English language decided that centuries ago.
The orders of magnitude question is also straightforward. You multiply by 10 for each order of magnitude larger and divide by ten for each order of magnitude lower.
0.1 is one order of magnitude lower than 1. 0.01 is two orders of magnitude lower, 0.001 is three orders of magnitude lower. (A 90% reduction, a 99% reduction, and a 99.9% reduction.) There are no common - or even uncommon, to my knowledge - words for cutting to one hundredth or one thousandth.
ETA: To tenth is not a English word. Tenth has no verb form in English.
I think very few people who use ‘order of magnitude’ as a regular part of their speech would agree with you.
To me, and I think to most other physicists/engineers/people who use ‘order of magnitude’, an order of magnitude reduction would be understood as a reduction to a (one) smaller order of magnitude, for example from 1,000,000 to 100,000, which is a 90% reduction. As pointed out, this is consistent with a two orders of magnitude reduction being a reduction to 1/100th of the original, three orders of magnitude reduction being a reduction to 1/1,000th of the original, etc.
I asked four questions which all orbited around a central theme. I numbered them to make sure people would see all of them. You answered one of them without acknowledging the theme. I tried to give you the benefit of the doubt by assuming that maybe the answer you gave hinted at a way to answer the questions to which you didn’t respond.
It will be after I have tenned the number of people using it enough to get it added to whatever dictionary you consider authoritative. Not sure if you’ve noticed but it can be changed. 
I only use it when something has been reduce by 1/10th. That way you can say:“It was literally decimated” and start off two word-use arguments at once.
Argh, I had a whole bunch of replies typed up, and then started pulling together one final concrete mathematical example, which then caused me to realize that my brain has apparently decided to take a vacation because it’s Friday.
Honestly, I don’t know what the hell I was thinking.