According to The New International Dictionary of Testament Theology (NIDTT):
“A man is called a [disciple] when he binds himself to someone else in order to acquire his practical and theoretical knowledge. He may be an apprentice in a trade, a student of medicine, or a member of a philosophical school. One can only be a [disciple] in the company of a … master or teacher, to whom the [disciple] … generally had to pay a fee. An obvious exception to this is when [disciple] refers to spiritual dependence on a thinker long since dead.” It is interesting to note that Socrates avoided using this term in part because of “its impersonal and commercial associations.”
Upon reading these words, you likely thought, “That’s close, but not really what Jesus intended!” Keep in mind, however, that this was the manner in which most people living in that period understood the term disciple.