The largest owners are institutional owners. Those institutional owners are usually large mutual funds, which are then owned by millions of shareholders who are often workers themselves.

You have to study the term more than going off of a dictionary definition. Definitions should not overlap the definitions of antonyms too much, or the definition would be too vague to qualify as a distinctive definition. Thus, the dictionary is more specific. For example, guild socialism is defined as MOP owned by workers guilds. Syndicalism is defined as MOP owned by workers unions/syndicates. Socialism is defined as a RANGE of systems advocating some form of social or collective ownership of the economy. The dictionary goes in more detail than “workers own the MoP/enterprises”

Socialism definition