Mere and Merely are not extremely common but when these words come up, people have a hard time understanding what they mean. In general, you can replace them with “only”.
They can be put to good use in academic writing!
The mere idea made me shudder.It was a mere formality.With the merest suggestion of corruption, the entire project will be shut down.
He’s merely a secretary.I was merely suggesting that…This merely aggravates the problem.This procedure is merely a matter of form.It was merely a coincidence; there was no causal relationship.