In the context of skill or knowledge:
* Beginner: A person who is new to a skill or subject.
* Novice: Someone with little or no experience.
* Amateur: A person who engages in an activity for pleasure rather than professionally.
* Unskilled: Lacking in skill or ability.
In the context of control or power:
* Servant: A person employed to do household work.
* Slave: A person who is owned by another and forced to work.
* Subordinate: A person who is lower in rank or position.
* Subject: A person who is under the rule of a sovereign.
In the context of ownership:
* Owner: The person who has legal possession of something.
* Possessor: The person who has something in their possession.
* Holder: The person who has something in their care.
Other possible opposites:
* Apprentice: A person who is learning a trade or craft.
* Student: A person who is learning under a teacher.
* Follower: A person who supports or admires a particular leader or ideology.
It's important to consider the specific context of the word "master" to determine the most appropriate opposite.