in, an adjective, any

[GoldfishLord]

In a study of complimenting behavior in American English, researchers discovered that one of the most striking features of compliments in American English is the almost total lack of originality. An initial examination of a large corpus revealed surprising repetitiveness in both the object of the compliments and the lexical items used to describe them. On closer investigation, it was discovered that regularities exist on all levels and that compliments are in fact formulas. We may categorize 80% of all compliments in the data as adjectival in that they depend on an adjective for their positive semantic value. In all, some seventy‒two positive adjectives occur in the data. What is striking, however, is that of these seventy‒two adjectives only five (nice, good, beautiful, pretty and great) are used with any frequency. While most adjectives occur only once or twice in the data, these five adjectives occur with such frequency that of all adjectival compliments in the corpus two thirds make use of only five adjectives.

Source: a Korean English test.

1. What is the meaning of "in"?
2. Could "adjectives" be used instead of "an adjective"?
3. Does the use of the "an" in "an adjective" fit sense 4 below?

a:
4 — used like any to refer in a general way to people or things
A person who is sick can't work well. [=people can't work well if they are sick]
Source: https://www.britannica.com/dictionary/a

4. To me, the red part says that the five adjectives are used so much, so I think that "any" should be "some". Where am I wrong?

 

[teechar]

1. What is the meaning of "in"?

It's a very straightforward meaning! You can think of it as "in the context of".
For example, "In American English, people compliment behaviour by using certain adjectives".

2. Could "adjectives" be used instead of "an adjective"?

It could, but it may imply that more than one adjective is used in any compliment. Here, "adjective" is clearer because the writer is trying to focus on certain individual adjectives.

3. Does the use of the "an" in "an adjective" fit sense 4 below?

a:
4 — used like any to refer in a general way to people or things
A person who is sick can't work well. [=people can't work well if they are sick]
Source: https://www.britannica.com/dictionary/a

See above.

4. To me, the red part says that the five adjectives are used so much, so I think that "any" should be "some".

"Any" is stronger (more dramatic) than "some" in that kind of sentence.