Predominantly: The predominantly is used to describe the most part of something. Let say you are calculating the visitors of your blog. You check your statistics and find that the most of the users are male.
So to describe this data you will say, my blog users are predominantly male. This means your statistics show most parts of your users are males compared to females.
You use the word predominantly when you are comparing two data to see which hold the most part.
Here is an example that shows the Wikipedia editors statistics.
