The word "extension" refers to the act of increasing the length, duration, or range of something. It can also indicate the addition of something to something that already exists. In various contexts, "extension" can pertain to physical objects, such as an extension cord that allows electrical devices to be powered from a distance, or it can describe a time allowance, such as extending a deadline for an assignment.
The word "extension" comes from the Latin word "extensionem," which is a noun form of "extendere," meaning "to stretch out." This Latin word is a combination of "ex-" (meaning "out") and "tendere" (meaning "to stretch"). The word has evolved into its current form as it was adopted into English in the late 14th century.