Mor is the Hebrew name for Myrrh. It's origins are in Yemen, Somalia and Ethiopia. Myrrh is mentioned number of times in the bible, in contexts with cosmetics and perfumery.
Mor plain and simple is an old Gaelic female name, in fact, in Irish speaking Ireland, it was the most common girl's name. The Irish had plenty of native names and avoided using Saints' names out of respect, like God forbid a kid called Iosa (Jesus), yet for the Spanish the opposite prevailed. Each to his own.Anyhow, Mor can be Moirin (little Mor) as differentiated from Mairin (Maurin) or little Mary (Maire). They sound very similar in English. The fact that Mor is also Gaelic for big has nothing to do with the name. Ditto for Coilin Mor or the elder Collin.