"tough outer membrane surrounding the brain and the spinal cord," c. 1400, from Medieval Latin dura mater cerebri, literally "hard mother of the brain," a loan-translation of Arabic umm al-dimagh as-safiqa, literally "thick mother of the brain." "In Arabic, the words 'father,' 'mother,' and 'son' are often used to denote relationships between things" [Klein].
late 14c., Latin, literally "nurturing mother," a title given by Romans to certain goddesses, especially Ceres and Cybele, from alma, fem. of almus "nourishing," from alere "to nourish, rear, support, maintain" (from PIE root *al- (2) "to grow, nourish") + māter "mother" (see mother (n.1)). The use of the Latin phrase for "one's university or school" is attested from 1710.
"nacreous inner layer of the shell of various bivalve mollusks," c. 1500, translating Medieval Latin mater perlarum, with the first element perhaps connected in popular imagination with obsolete mother (n.2) "dregs." Compare Italian madreperla, French mère-perle, Dutch parelmoer, German Perlmutter, Danish perlemor. It is the stuff of pearls but in a layer instead of a mass.