How do you know if a word in French is feminine or masculine?
Are there any rules, or is it just something you have to memorize? This is what I'm having the most trouble with right now! Merci :)
As others have said, you just need to memorize them. And you may well end up googling it more than ten times. (Use a reputable source like Larousse or AF if you do look them up.) Also, don't think it translates between languages, since I notice that you're learning Spanish. La nariz (the nose) is feminine in Spanish but le nez is masculine in French. El mar (the sea) is masculine in Spanish but La mer is feminine in French. Eventually you will find patterns (words in -tion or ité are always feminine), but it's better if those patterns are discovered by you naturally as you progress.
Although there're indeed certain patterns as mentioned. It's likely they're not gonna be of much help :).
Like some of the masculine endings are: -aire, -asme, -é, -eau, -et, -ien, -isme, -in, -nt, -oir, -age
While some of the feminine are: -ade, -aison, -ance, -ande, -ence, -ise, -son, -té, -tié, -ture, -ude, -tion, -esse, -ette, -ie, -ée
And as you can see it's not that likely that one would keep it all in mind when it's needed. Not to mention that by its sound alone it's quite often not even clear what the ending is anyway. And that even with those there are exceptions. Like prélude, interlude, rétrograde, stade are masculine despite the endings while cage, page, plage, rage and image are feminine.
If you already know a different romance language (e.g. Spanish, Portuguese, Italian, Latin) then mostly the genders are the same, so you can make a good guess. Also, some word endings are similar: une abeille = una abeja. Both feminine, and the “-eille” ending nearly always translates into “-eja”. As Angus notes above, there are a bunch of exceptions, but it works as a general rule.