Thayer's Greek Lexicon

 1. a burden, load
  1) of the freight or lading of a ship
2. metaph.
  1) of burdensome rites
  2) of the obligations Christ lays upon his followers, and styles
a "burden" by way of the contrast to the precepts of the
Pharisees, the observance of which was most oppressive
  3) faults of the conscience which oppress the soul

For Synonyms see entry G5819