/
ˌmagnəm ˈəʊpəs,
ˈɒpəs/
n.
(pl. magnum opuses or magna opera
/ˌmagnə ˈəʊpərə, ˈɒpərə/
)
a work of art, music, or literature that is regarded as the most important or best work that an artist, composer, or writer has produced.
Etymology
C18: from L., ‘great work’.