Partie vs. portion vs. part vs. morceau

The French language has several words to describe parts or pieces of a whole, such as 'partie', 'portion', 'part' and 'morceau'. Each word, although seemingly similar, has its own unique context and usage in the language.

Partie

'Partie' refers to a part or section of something that is considered as a distinct unit within a larger context. It can be abstract or concrete.
Elle joue une partie importante dans le projet.
(She plays an important part in the project.)
Nous avons regardé une partie du film.
(We watched a part of the movie.)

Portion

'Portion' emphasizes the concept of a part of a larger whole, often used in relation to food portions, but can also extend to non-material quantities.
Il mange une grande portion de gâteau.
(He eats a large portion of cake.)
Une portion de ses revenus va aux œuvres de charité.
(A portion of his income goes to charity.)

Part

'Part' generally refers to a share or role in something. It has a somewhat formal or literary tone and is versatile in usage.
Chaque membre doit faire sa part du travail.
(Each member has to do their share of the work.)
Il a vendu sa part de l'entreprise.
(He sold his share of the company.)

Morceau

'Morceau' refers specifically to a piece or bit of something more tangible, and is often used with food, music (pieces), or parts broken off from something larger.
J'ai mangé un morceau de chocolat.
(I ate a piece of chocolate.)
Elle joue un morceau au piano.
(She plays a piece on the piano.)

Summary

'Partie', 'portion', 'part' and 'morceau' all translate into English as part, piece or portion, but their use varies depending on the context - 'partie' for distinct units within larger contexts, 'portion' for parts of wholes, especially in servings, 'part' for shares or roles, often with a formal tone, and 'morceau' for tangible chunks or pieces.