This word is the past participle of the verb mittere, meaning "to send." It can be used as a noun, adjective, or even a verb itself depending on the context.
For example:
* Missus Dei - The sent one of God (referring to Jesus)
* Legatus missus - An ambassador sent (a messenger sent on a diplomatic mission)
* Missus ad explorandum - Someone sent to explore
* Missus est ad nos - He was sent to us
It's worth noting that the word "mission" itself comes from the Latin word "missio," which literally means "the act of sending."