While it is common to form adverbs by adding "-ly" to adjectives, there are plenty of adjectives that end in "-ly", usually by adding it to nouns: lovely, shapely, orderly, homely, etc. There are also examples of other words that function as both, especially adverbs of frequency. Hourly can be used as both an adverb and an adjective. So can daily,weekly, monthly, etc.

While I agree that sense of humor would be pluralized as senses of humor, it's a little more complicated than that. Sense of humor is an abstract noun or noun phrase. In many cases, it is not countable and should be treated as a mass noun. For example, "Our sense of humor is what separates us from the animals." I would use "senses of humor" only in cases where I was differentiating between two different senses of humor. Even then it could probably go either way, singular or plural, and still be correct. Try loosely substituting "playfulness" and you'll see that "playfulnesses" will rarely make better sense.

Also, court-martial can be pluralized as both courts-martial and court-martials. And for time-out becoming times-out? I don't think so. It's hyphenated, and can even be written as the single word, timeout. The plural is usually timeouts.

I've noticed that a number of books I've read from 1940's and before, from the UK, use "hallo" rather than "hullo" or "hello".

Head? I love it. That's great, especially since I never would have thought of it, but it is so familiar and obvious once you see an example. Ok, I've thought of a few and been playing with Google, so here are a few good ones I found:

Head, moose, elk, trout, salmon, tuna, shrimp, squid (a lot of animals, eh?), series, species, aircraft, hovercraft, cannon, offspring, you.

Some of the words I mentioned can be pluralized with or without the -s. I purposely did not list words whose plural is spelled the same but pronounced differently (like chassis or corps). I also tried to avoid mass nouns (although, offspring may be questionable. One could make a case for it really being a mass noun). I tried to avoid plural words that describe singular things (like pants and scissors). I was tempted to add "hair", since it can be singular and seemingly plural, but when used without an -s to mean more than one hair, we're back to a mass noun again, and, therefore, singlular.

What fun.

While I just posted something similar in a related topic, I'd like to ask the same thing in reverse:

How would you write “point two five percent” using only arabic numerals and symbols?

Answer: .25%

How would you write “a quarter of a percent” using only arabic numerals and symbols?

Answer: 1/4%

Kinda makes you think, doesn’t it?

Oh, and to make the analogy complete, how would you write "four and five tenths percent" using only arabic numerals and symbols?

Answer: 4-5/10%

For those of you who insist it should be "four and nine hundred seventy five thousandths percent" or something similar. Here's something to consider. Let's say we ask a few simpler questions in reverse:

How would you write "four point five percent" using only arabic numerals and symbols?

Answer: 4.5%

How would you write "four and a half percent" using only arabic numerals and symbols?

Answer: 4-1/2%

Kinda makes you think, doesn't it?

Let me give you an example that might clarify, not about percents, but illustrates the same idea. If someone asked you what the value of pi is, 3.14159..., you'd say "three point one four one five nine...." No one in there right mind would say "three and fourteen thousand one hundred and fifty nine, one-hundred-thousandths...approximately." Yes, I realize this isn't exactly the same thing, but you'd certainly never be wrong by just reading or writing out the digits (unless there were some legal principle or organizationally-required style manual involved).

If I were reading it out loud and wanted to be literal, I'd probably say "point two five percent". Actually, I'd expect to see it as 0.25% with a leading zero, and read it accordingly. If I were referring to the quantity, not actually reading it aloud, I'd probably say "a quarter of a percent", especially in casual speech. It also depends on the context. Somewhere on this site there's a lengthy discussion on this. By the way, I think this is one of those questions with many correct answers.

Cecily, perhaps I wasn't clear or you may have misunderstood. Orientate might be unremarkable in the UK, but that wasn't my point. Orientate is not unremarkable everywhere. Orient is.