1a) an opponent in a suit of law
1b) an adversary, enemy
Part of Speech: noun masculine
Citing in TDNT: 1:373, 62
From G473 and G1349; an opponent (in a lawsuit); specifically Satan (as the arch enemy): - adversary.
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 ἀντίδικος; click on the second column to search for that grammatical form of the root ἀντίδικος; click on the third column to search for that word and grammatical form; click on the total to search for the root ἀντίδικος.