1) prone to slander, slanderous, accusing falsely
1a) a calumniator, false accuser, slanderer
2) metaphorically applied to a man who, by opposing the cause of God, may be said to act the part of the devil or to side with him
Part of Speech: adjective
Citing in TDNT: 2:72, 150
From G1225; a traducer; specifically Satan (compare [H7854]): - false accuser, devil, slanderer.
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 διάβολος; click on the second column to search for that grammatical form of the root διάβολος; click on the third column to search for that word and grammatical form; click on the total to search for the root διάβολος.