Naming system -"ylene" There are various compounds which have common names that end in "ylene", like acetylene and ethylene. However, how come acetylene is an alkyne whereas ethylene is an alkene. Both of these have the same "ylene" ending though. What is the cause for this discrepancy?
These are common names, and predate our knowledge about bonds. My guess is that the "ylene" comes from reduction -- reducing ethyl alcohol gives ethylene, reducing acetic acid  gives acetylene.