Thayer's Greek Lexicon

 1. to guard, protect by a military guard, either to prevent hostile
invasion, or to keep the inhabitants of a besieged city from flight
2. metaph.
  1) under the control of the Mosaic law, that he might
not escape from its power
  2) to protect by guarding, to keep
  3) by watching and guarding to preserve one for the attainment of
something