Voted Best Answer
Mar 18, 2015 - 09:43 PM
It's because all the days end with "s" except domingo and sábado :) So you wouldn't say Los Luness, Los Martess, etc.. Since domingo doesn't end with "s" you have to add an "s" to "plurialize" it ! And it is "los domingos and los sábados" not "domingo's".