1) a herald or messenger vested with public authority, who conveyed the official messages of kings, magistrates, princes, military commanders, or who gave a public summons or demand, and performed various other duties. In the NT God's ambassador, and the herald or proclaimer of the divine word.
Part of Speech: noun masculine
Citing in TDNT: 3:683, 430
From G2784; a herald, that is, of divine truth (especially of the gospel): - preacher.
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 κῆρυξ; click on the second column to search for that grammatical form of the root κῆρυξ; click on the third column to search for that word and grammatical form; click on the total to search for the root κῆρυξ.