Today’s morning name was the Italian phrase il mio tesoro, and there’s no mystery where it came from: on my overnight iTunes, the 1959 Carlo Maria Guilini recording of Don Giovanni had reached Luigi Alva singing “Il Mio Tesoro” just as I woke. What was odd was that my still sleep-addled brain was puzzling over why Don Ottavio was calling Donna Anna his thesaurus.
Attribute it to an overactive mental-association apparatus connecting It. il tesoro ‘treasure’ (but also ‘darling, honey, dear’) to Engl. thesaurus referring to a specialized type of dictionary (derived ultimately from Greek). In this case, one reproducing a historical connection between It. tesoro ‘darling’ and It. tesoreria ‘thesaurus’, which are, etymologically, second cousins, more or less.
After this, on to the aria, with performances by Alva, Araiza, and Domingo.