The word root of memorialize is "mem".
A word root is the part of a word that carries its basic meaning. This meaning can be changed by adding different prefixes and suffixes. The root is considered the primary lexical unit of a word. In the word "memorialize", which means to commemorate, the word root is "mem". At the same time, "mem" means to remember and it is the word root of other words besides "memorialize", such as "memorable" and "memorial".