When it comes to the correct spelling between “extention” and “extension,” know that “extension” is the right one. “Extention” is a misspelling made so often that even native English speakers will write it this way.
For all intents and purposes, “extension” means to show how a device or component has the capacity to prolong or elongate something. For instance, there are hair extensions, extension cords, telephone extensions, and extension schools. All of these indicate a long-distance connection that the extension makes possible.
But, the confusion for this is understandable. This is due to the fact that both –sion and –tion are acceptable suffixes to add to nouns. Plus, both indicate “a state of being.” Therefore, it would stand to reason that you would add –ion to the root word “extent.” But, this isn’t true because “extent” is a noun.
When using these, you are essentially changing a verb into a noun. But, there are specific grammatical rules depending on what letters comprise the end of the verb. It’s what determines the use of –tion or –sion.
-SION for -END Verbs
For –sion, the verb must have –end. This is the correct form for “extension” because its root verb is “extend.” Other words include:
Ascend = Ascension
Distend = Distension
Suspend = Suspension
-TION for -ENT Verbs
When a verb ends in –ent, then you would add a –tion. Such is true for the following examples:
Indent = Indention
Prevent = Prevention
Circumvent = Circumvention
But here’s where the confusion comes in. People mistakenly think the root of “extension” is “extent.” But that is a noun connecting to the verb “extend.” For instances of doubt, keep a dictionary handy for when things get confusing.
When you want to remember which is the correct spelling between “extension” or “extention,” always refer to the root word. In this case, it will be the verb “extend.” Most verbs that end in –end will have the ability to change into a noun by removing the “d” and adding “–sion.”
While there are some exceptions to the rules of –tion and –sion, “extension” isn’t one of them. So, to keep things clear and concise, just remember that verbs ending in –end will use –sion to expand the meaning and create a noun. Remember that extension is correct and extention is incorrect.