magnum opus

/ˌˈmægnəm ˌoʊpəs/

Your magnum opus is your greatest piece of work. The Mona Lisa might have been Leonardo da Vinci's magnum opus, but your magnum opus is your western omelette.

In Charlotte's Web, Charlotte refers to her egg sac as her magnum opus, the "finest thing she has ever made," and that pretty much captures the spirit of this Latin phrase meaning "great work." Usually used for an artist's or author's greatest work, it can also be used ironically to refer to other great works — like your reorganized closet or your poem to your valentine.

Definitions of magnum opus

1. noun

   a great work of art or literature
   type of:

   work of art

   art that is a product of one of the fine arts (especially a painting or sculpture of artistic merit)