The difference between “an” & “année” (Year) is the same as “jour” & “journée” (Day), “matin” & “matinée”(morning) , “soir” & “soirée”(evening) ; In fact, it is just a question of considering time.
“An” , “Jour”, “matin”, “Soir”
are masculine words; You say un an/ un jour/un matin/ un soir
indicate a simple amount of time
have a more general meaning
Ex: Je suis restée 3 jours à Paris I stayed 3 days in Paris Ex: Il a 20 ans He is 20 years old
2. “Année”, “journée”, “matinée”, “soirée”
are feminine words; You say une année/une journée/une matinée/une soirée
indicate a duration of time
are usually stressing the actual length of time
Ex: J’ai travaillé toute la journée I have worked all day longEx: Passons la soirée tous les deux! Let’s spend the evening together!