duration vs longueur

duration and longueur both are nouns.

Word	Noun	Adjective	Verb	Adverb
duration	Yes	No	No	No
longueur	Yes	No	No	No

As nouns, longueur is a hyponym of duration; that is, longueur is a word with a more specific, narrower meaning than duration:

duration: the period of time during which something continues
longueur: a period of dullness or boredom (especially in a work of literature or performing art)

Other hyponyms of duration include clocking, residence time, span, stint, stretch, time scale, note value, time value, value, rule.

duration (noun)	longueur (noun)
continuance in time	a period of dullness or boredom (especially in a work of literature or performing art)
the property of enduring or continuing in time
the period of time during which something continues