I ban my students from using certain words in the IELTS test. The easiest way for me to explain why I ban these words is that most native speakers wouldn't use them if they were doing the test. Here are a few of my least favourites:
- Moreover - Native speakers hardly ever use this word, and students tend to use it wrongly. Just use 'furthermore' or 'also'.
- Demerits - It's ok to talk about the 'merits' of something, but the word 'demerits' seems unnatural. Just use 'disadvantages' or 'drawbacks'.
- Hence / Thusly - These words sound too formal and old-fashioned. Just use 'therefore' or 'as a result'.
Remember that topic vocabulary is the key to a high score, not 'difficult' words.