A well-known evangelical church in London refuses to call their 46 members who have been sent abroad "missionaries." They prefer instead "mission-partners." They realize that the "mission field" is all around them, and they go out to make friends with them, not with any hidden motive but simply to share with them the love with which Jesus has loved us all. All -- sent and senders alike -- are partners in mission.
The problem in using the term "missionaries," as in "This Sunday our guest speaker will be a missionary," is that it implies that we are not all missionaries. Such a mindset makes us oblivious to the field all around us and to our responsibility to share the Good News with others.
I think I'll start using that wonderful expression from now on: mission-partners.