What is the meaning and etymology of the (slang?) word まめ?

Question

私はあまりまめに書きませんが、ことばを学ぶのは大好きです。

I don't write that well, but I love learning the language.

What is the etymology of the word まめ here and what specifically does it mean?

My friend gave me this explanation:

「まめに書きません」＝そんなによく書きません、あまり書きません、規則正しく書きません.

まめに働きます＝まじめに一生懸命働きます」という言い方もあります。

I guess まめ is a colloquial word meaning to do well or do diligently?

Answer 1

mame (ni) expresses the way in which one seriously works hard at something without complaining about the task. Often you may translate it as "diligent(ly)".

There is another common usage meaning "healthy" as in mame ni kurasu "to live healthy".

You may see it written as 忠実 or 実.

The word is not new; it's been around for many hundreds of years, so I would not say that it is slang.

Links: Daijirin, Daijisen.