meaning of the word "complex"

What is the meaning of the word "complex" in the following sentences?
1. Non native English speakers often try to use complex words when they are speaking, but they use the words in the wrong context, thus I can't understand what they are saying.
2. When students take the essay part of the TOEFL test, they often use complex words. These students should know that a word may be complex, but it won't necessarily help them get a higher score. In fact, a simple word may be a better choice for them to use.
I'm having trouble thinking of a good definition for the word complex. I think it means a "big" word, or a word that isn't often used. Can you please tell me a better definition.

This is a good question, because often the meanings of words have layers that articulate the meaning greatly, though they arise from the same core meaning.

The way complex is used here, there could be several meanings as to what qualities the complex words have.

- Yes, often big words are considered complex; words that have many syllables or are difficult to spell.

- Uncommon words are often considered complex -- in any language. Sometimes people just don't use them and they are just unfamiliar. But sometimes, they're not used often because they are complex. And sometimes a very complex word becomes popular and no one knows what they are talking about cause they don't really know what the word means.

- Also, new words in English -- more important than simply slang -- are being born all the time. It's always good to have "The Urban Dictionary" saved to your favorites to use as a reference beyond Websters.

- There are many other qualities that make words complex - at least for some people, or some of the time. I often meet native English speakers, though, who don't seem to know the exact or complete meaning of many of the words they're using; they may even have the meaning of a word confused with the meaning of another word.

- So, because there are so many things that could make a word complex, I think we just have to conclude that any word that more difficult to understand than a lot of others is complex. It can have four letters, or eighteen letters. It can be based in Latin or Greek, or a Native American language, or Spanish or French or German. It can be slang or street language. It can be Internet English. It can be the vocabulary restricted to physics, or linguistics, or biology or software inventor geeks. Or combinations of many of these. Some are complex, some are simple. Some are "elegant," i.e. complex, but also simple.

I'm sorry I don't have access to a TOEFL vocabulary list at the moment. If you'd like to show me some words you find complex, or like to use and don't feel that you should have to be so careful about using them, I'd be glad to go over some vocabulary with you if you are studying for the TOEFL now.

Speaking for myself, as an American native speaker of English, I find that there is usually a word or pair of words I might tend to have trouble with at any given time. Maybe trouble pronouncing, or spelling correctly, or totally understanding all the meanings and uses of. Or sometimes I get words confused.

About 20 years ago, I remember I had these two words confused often when I would be talking. If I was writing, I would have time to look it up.

Antidote and Anecdote : this is just a bit amusing because the only thing they have in common is they both end with "dote" and begin with "a." This is not all THAT similar! It was just a little thing I stumbled upon whenever I was speaking. It was not a problem writing or reading them and understanding the difference.

- Antidote = a medicine against a poisonous bite, or a cure or answer to an ailment or problem - physical, technical, scientific, philosophical, metaphorical, behavioral, etc.

- Anecdote = a little story or the relation of an event or thought that is an offshoot or result of a larger thought or conversation.

I think a few people in most languages would admit to getting words a bit crossed now and then, and that it is not so unusual.

So evidently, you need to make a list of words that you have difficulty with, or words that you feel have elevated your vocabulary in the past year and/ or six months, and check yourself on them - see if your understanding of them is complete and near to exact. If it is, then go next to those words you find challenging and interesting now, and check yourself on those. Be sure to use both Websters and the Urban Dictionary on them, and use them in some sentences. Don't forget to learn the multiple meanings.

Remember, the entomology of a word can help you remember its meaning and spelling if you know any other languages like Latin or Greek, French etc.