In Middle English, the word hemp was stylized hempe, hemppe, henpe, henoppe, henepe, henep, and hanep. That's from Old English hænep, which traces to Proto-Germanic hanapiz, with the same definition. It's uncertain where that comes from, but it's definitely not Indo-European. The currently reigning theory is that it could be borrowed from a Scythian word sounding something like kannapis. That same word, linguists say, later evolved into Ancient Greek kannabis, which also referred to the plant. You can see where that is going: kannabis evolved into the Latin word cannabis, which was borrowed into English as the synonym for hemp. Hemp used to be used a lot more in literature, but now both are about equal; searches in Google Trends and uses in Google NGrams are about equal.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.