These are the 10 largest seas in the world according to ThoughtCo. as of 6/19/2020 A.D. The link to my source is here: https://www.thoughtco.com/largest-seas-on-earth-4164135
The term "sea" is very nebulous and can mean many things so if you want it defined go to my source.
Interesting list and nice game. The definition of what a sea is may be nebulous, but when it's called one it might be expected to count here (the Arabian Sea is almost four times the size of the Mediterranean). When is a sea not a sea? It could be argued: when it's called something else, like gulf or a bay...
To be quite honest I have no idea what the makers of the list I used consider a sea and not a sea. I'm guessing the people that made the list I used probably just looked at a map and only included seas that they could clearly define.
Then maybe that's just not a credible source. Perhaps it would be better to use a source (or multiple sources in order to get some sort of consensus) that has more clearly defined criteria for what makes a sea.
Have to agree with NigelS. Why isn't the Arabian Sea on this list? It's much larger than any of the others and it's actually called a sea, unlike two of your other answers.