EtrogThe Etrog is used with the Lulav, Hadas (myrtle) and willow branch (Arava) at the Feast of Tabernacles, or Sukkot . Of the Four Species of plants enumerated in Lev. xxiii. 40 , on which the carrying of the lulav is based, tradition takes "the fruit of the goodly tree" ( , properly "the fruit of a fair or noble tree") to designate the citron.
The citron (κίτρον, κίτριον); Citrusfruit of a tree of the orange and lemon family. It is oblong in shape, and sometimes as much as six inches in length. The skin is thick, somewhat hard, fragrant, and covered with protuberances; the pulp is white and subacid. Modern naturalists assume the north of India to be its native home; but it passed to the countries of the Mediterranean from Media or Persia ; hence the name of the tree, "Citrus medica," and of the fruit, "Malum medica," or "Malum Persica"
Based on content from 1901-1906 Jewish Encyclopedia. Please update as needed.