Today's word is mater, "mother." This is a word easy for English-speakers to learn and remember, and it is also one of those words that shows how closely related the words of different Indo-European languages can be: mother in English, mater in Latin, μήτηρ in Greek, мать in Russian, etc.
This is an extremely productive root in Latin, giving rise to such words as maternus (the adjectival form of mater), matercula (diminutive of mater), materfamilias (a word parallel in formation to paterfamilias), matrona (parallel to patronus), matrimonium (which gives us English "matrimony"), matertera (maternal aunt, as opposed to the paternal aunt, amita), materia (from which we get the word "material").
The related word matrix means, literally, a pregnant animal. Later on it came to mean the womb. The word matrix also means a source of information in the sense of a register or list, and from the diminutive, matricula, we get the English word "matriculation." In later Latin, the adjective matricalis meant something inventive or original, which is where we get the word "madrigal," meaning an ingenious type of musical song.
Here are some examples of today's word in Latin sayings and proverbs; for more information, see the page at the Scala Sapientiae, which contains notes on some of the proverbs cited below, as well as additional proverbs:
Natura rerum omnium mater.
Mater semper certa est, pater numquam.
Qualis mater, talis et filia.
Sicut mater, ita et filia eius.
Ut pater, ita filius; ut mater, ita filia.
Filius ut patri similis, sic filia matri.
Terra est communis mater omnium mortalium.
Mater bonarum artium est sapientia.
Voluptas malorum mater omnium.
Matris imago filia est.
Mater criminum necessitas.
Mater artium necessitas.
Nemo non formosus filius matri.
Timidi mater non flet.
Mater timidi flere non solet.
Terra mater crescentium, nutrix viventium.
Luxuria avaritiae mater.
Honora patrem tuum et matrem tuam.
Luxuria inopiae mater.