Thayer's Greek Lexicon

 1. anything established, anything received by usage, a custom, a law,
a command
  1) of any law whatsoever
1a1. a law or rule producing a state approved of God
1a  1) by the observance of which is approved of God
1a2. a precept or injunction
1a3. the rule of action prescribed by reason
  2) of the Mosaic law, and referring, acc. to the context. either
to the volume of the law or to its contents
  3) the Christian religion: the law demanding faith, the moral
instruction given by Christ, esp. the precept concerning love
  4) the name of the more important part (the Pentateuch), is put
for the entire collection of the sacred books of the OT