n.
   - an important assignment, typically involving travel abroad. ▸
[treated as sing. or pl.]
 a group of people sent on a mission. ▸an organization or institution involved in a long-term assignment abroad. ▸a military or scientific expedition. 
- the vocation of a religious organization to spread its faith. ▸a building or group of buildings used by a Christian mission. 
- a strongly felt aim or calling.
Etymology
  C16 (denoting the sending of the Holy Spirit into the world): from L. missio(n-), from mittere ‘send’.