Noun
etrog (plural etrogs or etrogim)
(Judaism) The yellow citron (Citrus medica) used in Sukkot ritual.
For that reason, the rabbis ruled that one should not take the lulav and etrog on the eighth day, even outside of the Land of Israel. Source: Internet
Shulchan Aruch, Orach Chayim 668 However, one does not take the lulav and etrog (nor does one sleep in the sukkah according to most opinions) on the eighth day. Source: Internet
If someone sees a neighbor on the street with a lulav and etrog on the eighth day, the rabbis reason, s/he might mistakenly assume that it is still the seventh day (ḥol hamoed), when the lulav and etrog are still needed. Source: Internet
Rabbis may rule that a specific mitzvah from the Torah should not be performed, e.g. blowing the shofar on Shabbat, or taking the lulav and etrog on Shabbat. Source: Internet
The lulav and etrog are not brought to the synagogue on Shabbat. Source: Internet