1) a delegate, messenger, one sent forth with orders
1a) specifically applied to the twelve apostles of Christ
1b) in a broader sense applied to other eminent Christian teachers
1b1) of Barnabas
1b2) of Timothy and Silvanus
Part of Speech: noun masculine
Citing in TDNT: 1:407, 67
From G649; a delegate; specifically an ambassador of the Gospel; officially a commissioner of Christ ("apostle"), (with miraculous powers): - apostle, messenger, he that is sent.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root ἀπόστολος; click on the second column to search for that grammatical form of the root ἀπόστολος; click on the third column to search for that word and grammatical form; click on the total to search for the root ἀπόστολος.