Other forms: longueurs
A longueur is a section of a book or movie or play that's really tedious or boring. You might love the movie "West Side Story," except for the longueur of the dream sequence that features a ballet dance.
You'll often come across this word in its plural form, longueurs, as when a book reviewer notes the longueurs of a writer's descriptions of the English countryside, or your aunt starts to snore during the longueurs of a play's third act. You can use this noun for any dull spell, but it's mostly a literary or performing arts term, from the French longueur, "length," and the Latin root longus, "long."