Opus (noun)

1. A piece of music, literature, or art, typically one that is considered the most important or best work of an artist or composer.
2. A piece of work, especially a literary or artistic production.

Origin:

Early 17th century: from latin, literally "work", from opus, oper- "work", from the verb operari "to work".

Examples:

1. Beethoven's ninth symphony is considered his greatest opus.
2. The artist's latest opus is a series of large canvases.
3. The writer's opus is a collection of short stories.
4. The composer's opus is a collection of piano pieces.
5. The architect's opus is a monumental building.