The longer form année
does not imply a special occasion. It is used to stress the period's duration. Roughly speaking, an
is the point in time (J'ai cinquante ans
), and année
is the period (Il faut compter une année pour voyager à Mars
). The same goes for nuit
/nuitée
, matin
/matinée
, soir
/soirée
, jour
/journée
.
Note: a similar distinction is found in e.g. cuiller (or cuillère)
vs cuillerée
, where the former simply denotes a spoon, and the latter the volume it can contain (spoonful, as in recipes). Other examples include bouche
/bouchée
and bol
/bolée
. It is, generally speaking, a way of expressing an entity's extension in space or time.