Question: Cambridge Dictionary gives this definition about "complain"

> 
> to say that something is wrong or not satisfactory
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and this definition about "complaint"

> 
> a statement that something is wrong or not satisfactory
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I guess both of them means the same thing. However, [Google Ngram](https://books.google.com/ngrams/graph?content=to%20complain%20about%2C%20make%20a%20complaint%20about%20&case_insensitive=on&year_start=1800&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cto%20complain%20about%3B%2Cc0%3B.t1%3B%2Cmake%20a%20complaint%20about%3B%2Cc0#t1%3B%2Cto%20complain%20about%3B%2Cc0%3B.t1%3B%2Cmake%20a%20complaint%20about%3B%2Cc0) shows that the former is much more commonly used that the latter

[![enter image description here](https://i.stack.imgur.com/IyIrh.png)](https://i.stack.imgur.com/IyIrh.png)

Are those two expressions interchangeable?

Answer: 
In relative , noun or adverbial clauses we often face these kinds of sentences. E.g “Who I am is not important.
You have two ideas together. One is that the conclusion *is* right. The other is that both A and B *are* harmful. You are putting these into one sentence and finding it troublesome. 

You are also rushing by with spoken English and leaving out an implied word that explains things.

The conclusion is *that* both are purple.