What's the difference between 词典, 辞典, and 字典? I don't think they are necessarily different kinds of dictionaries, but is there a subtle distinction? Or maybe their etymologies?
字典 means dictionary of characters. A common 汉字字典 should contain ~8000 entries for each Chinese character. In each character entry, it's often to see example words or short phrases using that character. So, it's common to see a 汉字字典 is used as a 汉语词典.

词典 means dictionary of words. So, each entry of a 汉语词典 is a word. Generally 汉语词典 is sorted in alphabetic order in Chinese characters, so it's common to see a 汉语词典 is used as a 汉字字典.

So, in China, there's not too much difference between 汉字字典 and 汉语词典. But the book of 汉语词典 is mostly thicker then 汉字字典.

辞典 means dictionary of phrases. Generally, 辞 may refer to some famous, well known phrases said by some dead guys or famous man. Well, like I've said it's not too much differences between 词典 and 辞典, but a book of 汉语辞典 is mostly thicker then a 汉语词典. You can also expect that a 汉语大辞典 is thicker then a 汉语辞典.

In English, it will be something like:

English 字典： (26 entries)

A    This is the first letter.
B    This is the second letter.
...
Z    This is the last letter.


English 词典:

A        Indefinite article. Also the first letter. e.g. a cat.
Apple    A kind of fruit. Green or red.
Cat      A white animal. two ears, four legs.
...


English 辞典:

Rain cats and dogs: A very big rain. Its rain drop is as big as cat or dog.


(Most 汉语辞典s include words and characters entries as well.)