There isn't a direct antonym for "sahib" in the same way there is for words like "good" and "bad." However, depending on the context, you could use words like:
* Servant: This refers to someone who works for another person.
* Subject: This implies someone under the rule or control of another.
* Underling: This is a more informal term for someone of lower rank.
* Commoner: This refers to someone who is not of noble birth or high status.
The best word to use will depend on the specific situation and the meaning you want to convey.