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.
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.