Etymology
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mother-of-pearl (n.)

"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.

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magna mater 

a fertility goddess, 1728, Latin, literally "great mother;" see magnate + mother (n.1).

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Mother Goose 
probably a translation of mid-17c. French contes de ma mère l'oye, which meant "fairy tales." The phrase appeared on the frontispiece of Charles Perrault's 1697 collection of eight fairy tales ("Contes du Temps Passé"), which was translated in English 1729 as "Mother Goose's Tales", and a very popular collection of traditional nursery rhymes published by John Newbery c. 1765 was called "Mother Goose's Melody." Her own biographical story is no earlier than 1806.
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Alma Mater (n.)

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)). In sense of "one's university or school," attested from 1710.

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dura mater (n.)

"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].

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Stabat Mater 
Latin Stabat Mater dolorosa "Stood the Mother (of Jesus) full of sorrow," opening words of a sequence composed 13c. by Jacobus de Benedictis.
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Tuatha de Danann 
1680s, from Irish Tuatha dé Danann, literally "the people of Danann," from plural of tuath (see Teutonic) + Danann, apparently originally an oblique case of Danu, mother of the gods.
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birthday suit (n.)
first attested 1730s, but probably much older. The notion is the suit of clothes one was born in, i.e., no clothes at all. Compare Middle English mother naked "naked as the day one was born;" Middle Dutch moeder naect, German mutternackt.
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Mothers' Day 
the spelling used in the U.S. congressional resolution first recognizing it, May 9, 1908.
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Roman holiday (n.)

"occasion on which entertainment or profit is derived from injury or death of another," 1860, originally in reference to holidays for gladiatorial combat; the expression seems to be entirely traceable to an oft-quoted passage on a dying barbarian gladiator from the fourth canto (1818) of Byron's "Childe Harold's Pilgrimage":

But where his rude hut by the Danube lay
There were his young barbarians all at play,
There was their Dacian mother. He, their sire,
Butcher'd to make a Roman holiday!
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