A black Brit on his way to the U.S. wants to know if his use of the word will be offensive—and whether he should care.“Niggardly.” Go on, I dare you. Say it. Savor those syllables. Let your tongue caress those consonants. If you’re black and reading this, you may well have just laughed, smiled knowingly, been confused or even taken offense, depending on the size of your vocabulary. If you’re white and reading this, you will probably have just experienced a mild frisson of linguistic danger, as you are either fully aware of the ramifications that your verbalizing the word...