1) a witness
1a) in a legal sense
1b) an historical sense
1b1) one who is a spectator of anything, e.g. of a contest
1c) in an ethical sense
1c1) those who after his example have proved the strength and genuineness of their faith in Christ by undergoing a violent death
Part of Speech: noun masculine
Citing in TDNT: 4:474, 564
Of uncertain affinity; a witness (literally [judicially] or figuratively [generally]); by analogy a "martyr": - martyr, record, witness.
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 μάρτυς; click on the second column to search for that grammatical form of the root μάρτυς; click on the third column to search for that word and grammatical form; click on the total to search for the root μάρτυς.