In languages with grammatical gender, like French, you can often get away with getting the genders wrong, although it’s best to try to learn them when you learn nouns. However there are some words that have different meanings in different genders.
An example in French is loup(e): le loup [lu:] (masculine) is a wolf, and la loupe [lu:p] (feminine) is a magnifying glass – the context will clarify what you mean if you get the genders mixed up, and the pronunciation helps as well.
The following French words have the same pronunciation but different meanings in different genders:
– le boum = bang, explosion / la boum = party
– le bout = tip, end / la boue = mud
– le cave = idiot, sucker / la cave = basement, cellar
– le chêne = oak tree/wood / la chaîne = chain, channel
– le col = collar, neck / la colle = glue
– le livre = book / la livre = pound (curreny/weight)
– le manche = handle / la manche = sleeve / la Manche = English Channel
– le mur = wall / la mûre = blackberry
– le rose = pink (colour) / la rose = rose (flower)
– le vase = vase / la vase = silt, mud
More words like this: http://french.about.com/od/vocabulary/a/dualgender_2.htm
One way to avoid getting your genders in a muddle is to talk about everything in the plural.
le Loir (a river) / la Loire (another river)
This is rare in German, but there are a few examples:
der Schild = shield / das Schild = signboard/plaque
der Kiefer = jaw / die Kiefer = fir tree
der Reis = rice / das Reis = small twig
das Pony = small horse / der Pony = bangs, fringe, that haircut
Interestingly, they are distinguished in the plural (even though genus is not overtly marked in the plural) – die Schilde vs. die Schilder, die Kiefer (yes, the plural nominative of the masculine conveniently looks like the singular nominative of the feminine) vs. die Kiefern.