In conversation, we use some words interchangeably, as if they meant the same thing. But if synonyms meant exactly the same thing, we wouldn’t need different words, would we? If we understand the distinctions, we know which choice is best.
A While or Awhile
Awhile is a noun referring to a period of time. After a preposition, a noun by itself makes no sense. We need an article a, an, or the preceding while. For example, we wouldn’t say, “For house,” but rather, “For the house.” Following the same principle, we don’t want to say, “For awhile,” but rather, “For a while,” using the two-word form after the preposition.
Give John awhile to make up his mind, and after a while we’ll have his decision.
Crucial or Critical
While the two might be used interchangeably, critical works best for extreme danger and crucial for something very important.
It may be crucial to pay bills on time, but when the debtor is about to be sued, his condition has become critical.
Day Before or Yesterday
The correct word and meaning depend on the point of view. Yesterday refers to the day before the present day in the story. The day before refers to whatever day precedes the current day in focus, which could be any day, even in the future.
Eldest or Oldest
Both eldest and oldest refer to age, but a distinction does exist. Eldest refers only to people in relation to two or more other people. If the comparison is with only one person, elder, is correct, although common practice seems to prefer use of older and oldest, which can work for age comparison of anything, including people.
Jim is the eldest sibling, but Jane is the elder of the two sisters. Jim drives the oldest car.
End or Ending
In conversation, people might use end and ending interchangeably, but you can probably sense a slight difference in meaning. End marks a point of conclusion with zero duration. The ending can be much longer. For example: The end of a book might be regarded as the last words on the last page, which said, “The End.” But the ending would be what comes after the climax, the last chapter, perhaps.
The end of a race is the finish line. The ending is that last sprint to achieve the best time.
Euphemism or Pretense
A euphemism is a substitute word or phrase for what might be otherwise regarded as unpleasant. A pretense represents something as other than what it really is. Instead of saying the mayor had died, reporters used euphemisms, saying, “He passed away,” “He departed this life,” or “He went to Heaven.”
He excused himself from the business meeting under the pretense that he had to make an important call.