tl;dr Are you aware of any dictionaries that explain word etymologies (not merely character etymologies)? Some links/references would be useful.
This is actually a collection of related questions, but I thought it would be good to keep them together.
Are there any online etymological dictionaries of Chinese? All such dictionaries I can find deal with character etymologies, which is not at all the same thing as the etymologies of the real spoken language (which can do just fine without a writing system at all, I'm sure that not more than a 100 years ago literacy rate in China was far from great).
Generally, how well do character etyomologies reflect the true etyomologies of words?
Let me give a motivating example, which made me curious about it. Yak in Mandarin is 牦牛 / 氂牛 / máoniú, i.e. when spoken sounds just like "hairy cow" 毛牛, a very fitting description. If it weren't for the characters, one would be tempted to suspect this is not an accident. Yet if we look up the character (not word!) online, we only get "signific cluster, an ox 牜牛 that requires couxing 攵攴 from a branch 未", which suggests otherwise.
To avoid an all too common misunderstanding, I'd like to point out again that although a writing system can leave a deep mark on the oral language, a language can exist just fine without it. I am sure that a 100 years ago the literacy rate in China was far below great, yet people could use the language just fine. So again, when I say Chinese in this question, I mean the spoken Chinese language (take whichever variety you prefer), not the character based writing system (I have the impression that often answers about Chinese consider written Chinese first).