aigre
sour
Les bonbons de citron ont un goût aigre.
The lemon candy has a sour taste.
Also, note that aigre-doux means sweet and sour.
TIP: An easy way to remember this word lies in remembering the part it plays in the word vinaigre, the French word for vinegar. If you break down vinaigre (vin + aigre), you’ll see that it is quite literally sour wine.