Gioconda

by 1827 as the name of Leonardo's painting or its subject, Lisa, wife of Francesco del Giocondo (see Gioconda). Mona is said to be a contraction of madonna as a polite form of address to a woman, so, "Madam Lisa." Mona Lisa smile in reference to an appealing but enigmatic expression is by 1899.

late 14c., "pleasing, gracious; joyful," from Old French jocond or directly from Late Latin iocundus (source of Spanish jocunde, Italian giocondo), variant (influenced by iocus "joke") of Latin iucundus "pleasant, agreeable," originally "helpful," contraction of *iuvicundus, from iuvare "to please, benefit, help, give strength, support," which is from a PIE source perhaps related to the root of iuvenis "young person" (see young (adj.)).

In jocose cheerfulness or light-heartedness is an accidental thing; in jocund it is the essential idea. [Century Dictionary]