Why is the Chinese word for "banana" "香蕉"? Where did it come from?
According to the 《國語詞典》，the「香」in「香蕉」came from the sweetness of its fruit （果實香甜）。Chinese etymology does not draw a clean line between the sense of taste and the sense of smell, which is pretty scientific when you think of the close relation between the olfactory and gustatory system. Therefore, the honeydew,「香瓜」, is also known as「甜瓜」. The meaning and etymology of「蕉」is much more complicated. The short answer will be, the term generally denotes plants belonging to the Musaceae family（芭蕉科）, of which the banana is a very well known member.
An addition to the @sati's answer about etymology of the character 蕉: according to the Outlier Dictionary, only the top part of the character 艹 (cǎo) is related to the meaning (semantic component) which is common for any kind of plants. And 焦 (jiāo) is merely a sound component. It means that you shouldn't search for a semantic connection between 蕉 and 焦: the latter just gives the pronunciation to the former.