The noun medium is of Latin origin and has been part of the English language since the 1580s.
If you look it up in a dictionary, you’ll see that it has two plural forms – media, which is in line with other Latin borrowings such as, for example, datum – data and bacterium – bacteria, and mediums.
Languages are mediums (=means) of interaction and communication.
You certainly know that we refer to all the people and organisations providing information and news for the
public, i.e. newspapers, radio, TV, etc., as the mass media and never the mass
The mass media is often referred to as the Fourth Estate.
Notice that the (mass) media is now often used as an uncountable noun with a singular verb, though Bernard C. Lamb, President of the Queen’s English Society, argues that is ‘wrong, wrong, wrong!’ He also insists mediums should only be used for people who claim to be able to communicate with the dead.
After his father died, he spent a small fortune on mediums trying to find out if his late parent was happy in the afterlife.
So if you want to speak impeccable English, you’d better listen to Mr Lamb. Besides, I think it’s the easiest way to remember when to use media and when mediums.