Most people first encounter “obtuse” in geometry class, where it labels an angle of more than 90 degrees and less than 180. Imagine what sort of blunt arrowhead that kind of angle would make and you will understand why it also has a figurative meaning of “dull, stupid.” But people often mix the word up with “abstruse,” which means “difficult to understand.”
When you mean to criticize something for being needlessly complex or baffling, the word you need is not “obtuse,” but “abstruse.”
Although it’s “absorbed” and “absorbing,” the correct spelling of the noun is “absorption.”
But note that scientists distinguish between “absorption” as the process of swallowing up or sucking in something and “adsorption” as the process by which something adheres to the surface of something else without being assimilated into it. Even technical writers often confuse these two.
“This isn’t about you.” What a great rebuke! But conservatives sniff at this sort of abstract use of “about,” as in “I’m all about good taste” or “successful truffle-making is about temperature control” ; so it’s better to avoid it in very formal English.
“AM” stands for the Latin phrase Ante Meridiem —which means “before noon”—and “PM” stands for Post Meridiem : “after noon.” Although digital clocks routinely label noon “12:00 PM” you should avoid this expression not only because it is incorrect, but because many people will imagine you are talking about midnight instead. The same goes for “12:00 AM.” You can say or write “twelve noon,” “noon sharp,” or “exactly at noon” when you want to designate a precise time.
It is now rare to see periods placed after these abbreviations as in “A.M.”; but in formal writing it is still preferable to capitalize them, though the lower-case “am” and “pm” are now so popular they are not likely to get you into trouble.
Occasionally computer programs encourage you to write “AM” and “PM” without a space before them, but others will misread your data if you omit the space. The nonstandard habit of omitting the space is spreading rapidly, and should be avoided in formal writing.
If you offer pie à la mode on your menu, be careful not to spell it “ala mode” or—worse—“alamode.” The accent over the first “a” is optional in English, although this is an adaptation of the French phrase à la mode de meaning “in the manner of.” The one-word spelling used to be common, but as people became more sensitive to preserving the spelling of originally French phrases, it fell out of favor. In whose manner is it to plop ice cream on your pie? Nobody really knows, but it’s yummy. Stick with the two-word spelling in all other uses of the phrase “à la” as well.
“A.D.” does not mean “after death,” as many people suppose. “B.C.” stands for the English phrase “before Christ,” but “A.D.” stands confusingly for a Latin phrase: anno domini (“in the year of the Lord”—the year Jesus was born). If the calendar actually changed with Jesus’ death, then what would we do with the years during which he lived? Since Jesus was probably actually born around 6 B.C. or so, the connection of the calendar with him can be misleading.
Many Biblical scholars, historians, and archeologists prefer the less sectarian designations “before the Common Era” (B.C.E.) and “the Common Era” (C.E.).
Traditionally “A.D.” was placed before the year number and “B.C.” after, but many people now prefer to put both abbreviations after the numbers.
All of these abbreviations can also be spelled without their periods.
You should use “an” before a word beginning with an “H” only if the “H” is not pronounced: “an honest effort”; it’s properly “a historic event” though many sophisticated speakers somehow prefer the sound of “an historic,” so that version is not likely to get you into any real trouble.
If the word following begins with a vowel sound, the word you want is “an”: “Have an apple, Adam.” If the word following begins with a consonant, but begins with a vowel sound, you still need “an”: “An X-ray will show whether there’s a worm in it.” It is nonstandard and often considered sloppy speech to utter an “uh” sound in such cases.
The same rule applies to initialisms like “NGO” (for “non-governmental organization”). Because the letter N is pronounced “en,” it’s “an NGO” but when the phrase is spoken instead of the abbreviation, it’s “a non-governmental organization.”
When the following word definitely begins with a consonant sound, you need “a”: “A snake told me apples enhance mental abilities.”
Note that the letter Y can be either a vowel or a consonant. Although it is sounded as a vowel in words like “pretty,” at the beginning of words it is usually sounded as a consonant, as in “a yolk.”
Words beginning with the letter U which start with a Y consonant sound like “university” and “utensil” also take an “a”: “a university” and “a utensil.” But when an initial U has a vowel sound, the word is preceded by “an”: it’s “an umpire,” “an umbrella,” and “an understanding.”