opus

opus /ˈoʊpəs/ noun
plural opera /ˈoʊpərə/ also opuses /ˈoʊpəsəz/
opus
/ˈoʊpəs/
noun
plural opera /ˈoʊpərə/ also opuses /ˈoʊpəsəz/
Britannica Dictionary definition of OPUS
[count]
1 
: a piece of music written by a major composer — usually singular — usually followed by a number (called an opus number) that indicates when a piece of music was written in the list of works written by the same composer
2 
formal : an important work done by a writer, painter, etc. — usually singular — see also magnum opus