The 1828 edition of Webster's Dictionary defines apostle as follows:
APOS'TLE, noun [Latin apostalus; Gr. to send away, to sent.] A person deputed to execute some important business; but appropriately, a disciple of Christ commissioned to preach the gospel. Twelve persons were selected by Christ for this purpose; and Judas, one of the number, proving an apostate, his place was supplied by Matthias. Acts 1:2.