Is it ensure, insure, or assure?
late 14c., Latin, literally "bountiful mother," a title Romans gave to goddesses, especially Ceres and Cybele, from alma, fem. of almus "nourishing," from alere "to nourish" (see old) + mater "mother" (see mother (n.1)). First used 1710 in sense of "one's university or school" in reference to British universities.
The school or university from which one graduated. The term also refers to a school's official song: “The reunion began with everyone singing the alma mater.” From Latin, meaning “nurturing mother.”