In Arabic their are two signs that indicates a feminine noun : * The " (التاء المربوطة (ة " [ Ta2 marbota] at the end of the word. For example : 7afela ( حافلة), Sayyara (سيارة), Shajara (شجرة) * The " (ألف مكسورة أو همزة (ى أو ء" [ Alef Maksoora or Hamza] at the end of the word. For example: sahra2 (صحراء), Salma (سلمى) These signs indicates that this word is feminine. But however, there are a lot of words that are just known to be feminine; for example " Ard (أرض)". And there is no way to indicate the gender of these words other than memorizing them.

Unfortunately I didn't find any dictionary that gives you the gender of nouns! So like Mahdi says you are supposed to memorize it....but if you do not know it how can you memorize it? Anyway I just would like to suggest two free and very useful resources online aratools.com it's an Arabic versus English dictionary, try it! there is also a great App for smartphones it's the famous Hans Wehr dictionary Arabic/English by roots, you can download it for free, it is called Arabic Almanac.