nounnounnounadjective

le demi

half · semi

C’est quand quelque chose est coupé en deux parties égales et on parle d’une seule de ces parties.

The French word demi is a versatile term that translates primarily to "half." It functions in several ways:

Adjective (Half): Used to denote one of two equal parts. For example, une demi-heure (half an hour).
Noun (Half-liter/Beer): In a bar setting, a demi refers to a 25-centiliter glass of beer (historically a half-liter, but the measure has shrunk over time in common usage).
Prefix: It is frequently used as a prefix (often hyphenated) to indicate something is partial, incomplete, or of a lower status, such as demi-tour (U-turn) or demi-sel (semi-salted).

Grammar:

As an adjective, it is invariable when placed before a noun (e.g., deux heures et demie vs une demi-heure). When it follows a noun, it agrees in gender (e.g., une heure et demie).
It is derived from the Latin dimidius, meaning "divided in the middle."