demi

In a sentence

• J'ai mangé une demi-pomme.

  I ate half an apple.

  Here, 'demi' is used as an adjective to indicate half of a specific noun, 'pomme' (apple). It is placed before the noun and agrees in gender but typically not in number. 'Demi' is connected with a hyphen when preceding the noun.

• Nous devons attendre une heure et demie.

  We need to wait an hour and a half.

  Here, 'et demie' is used adverbially to specify 'an hour and a half'. When referring to time, 'demi(e)' agrees in gender with the noun 'heure' (hour) and forms a construction that conveys an additional half unit.

• La salle était remplie à moitié, presque à demi.

  The room was half full, almost halfway.

  Here, 'à demi' is used adverbially to describe the state of 'remplie' (filled) with the meaning of 'halfway' or 'partially'. The phrase 'à demi' modifies the adjective and does not change according to gender or number.