Work and piece. In specific contexts it is common to find these two words used in combination, such as in this week's Metal Inspirations extract (or I could say:
piece). Work in the meaning of "práca" in the sense of "robota" is uncountable - people can do a lot of work, some work, or not enough work. In physics, work may be measured in ergs or joules
(don't ask me how!). Work in the meaning of "dielo", however, is countable - a work of art, an interesting work, the complete works of Shakespeare.
A work of art can be called a piece, especially a sculpture or a shortish musical composition, probably classical. Eine kleine Nachtmusik is one of Mozart's most
famous pieces. This meaning of piece should be clear from the context, which must be about art, because otherwise the normal meaning of piece is "kus" in the sense of "kúsok" (rather than "kus
tovaru"). Then there is "piecework", which is the system of paying workers for how many "pieces of work" they produce in one shift, rather than their hours of work.