La tigre, le tigri. You can get the gender from the articles, in this case it is feminine. Two similar examples, but with masculine gender: Il leone, i leoni. Il fiore, i fiori. Feminine gender: La vite, le viti. (vite: 1. grape plant, 2. screw) La nave, le navi. (ship) La mente, le menti. (mind) There is NO way to know it, unless you learned from a specific example, but if you are sure about the articles to be used, then you can also be sure about the gender of the nouns.

Grammarly, "tigre" is feminine, but it can be either a he-tiger or a she-tiger. If you need to specify the actual sex of the tiger, you have to say: MALE: "la tigre maschio" or "il maschio della tigre"; FEMALE: "la tigre femmina". In ancient Italian there was also the masculine "il tigre". Someone still uses it, but it's very uncommon.