et·rog 
(ĕtrōg, -rəg, ĕt-rôg)
(ĕtrōg, -rəg, ĕt-rôg)n. pl. et·rogs also et·ro·gim (ĕt-rə-gēm)
1. A western Asian tree (Citrus medica var. etrog) having white flowers and sour yellow fruit.
2. The fruit of this tree, used ceremonially in the Jewish festival of Sukkot.
[Aramaic and Mishnaic Hebrew 'etrōg, from Middle Persian wādrang, citron; akin to Sankrit māṭuluṅgam, from a source akin to Tamil mātaḷai, mātuḷai and Malayalam mātalam.]