Since they're so phonetically close and both pertain to moola, it's glaringly obvious now that stipend and spend are connected. The word stipend is from French stipende, which is from Latin stipendium, a shortening of stipipendium. All these etymons had the same definition, but that changed as we break up stipipendium into stips ("payment") and pendere ("weigh"; a lot of commerce was done by exchanging certain weights of goods. This word also had a secondary definition of "to hang", because weights hang. We've actually already seen this word before). Meanwhile, spend is curious because it took a very Germanic path into Latin: from Middle English spenden, from Old English spendan, and from Proto-Germanic spendana, it finally goes back to the Latin word expendere, or "to weigh out" (again we see the connection between mass and money), a combination of ex- ("out") and pendere, where we meet up with stipend. From here, pendere becomes Proto-Italic pendo, "hang", from Proto-Indo-European pend, also "hang".
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.