How to pronounce "Facetious"?

Hi there

Thank you for your question. 

If we had to write the word facetious in the way it should be pronounced, then it would be written as follows;   fuh-see-shuhs. You sound it out here exactly the way it is written. This is using phonetic spelling.

I hope this helps you. Should you require any further assistance, please do not hesitate to contact me and I will gladly assist you.