In linguistics, back-formation refers to the process of creating a new word by removing affixes from an existing word. To put it plainly, it means removing part of a word to make a new word. (The new word created by back-formation is also called a back-formation.) Most often, back-formation involves making a new verb from an existing noun: for example, cohabitation gave rise to the verb cohabitate, and vaccination to vaccinate.
A curious thing about back-formations is that they sometimes come into existence from the assumption that they already exist. Think about it: a word like cohabitation looks like –ion has been added to cohabitate, so cohabitate is imagined to be the source word from which cohabitation was derived. But in fact the opposite is true, and there are dozens of examples of this. Would you have guessed that the verb donate is a back-formation from the noun donation? Or that curate is derived from curator? Or that oration preceded orate? In many cases the back-formations have become so well established in their own right that we assume they’ve always been with us.
And while many back-formations are fully accepted—few people would bat an eye at resurrect (from resurrection) or at diagnose (from diagnosis)—others are met with skepticism because they are assumed to be neologisms. Some usage writers direct their ire in particular at back-formations ending in –ize: for example, words like randomize, incentivize, and legitimize. But many –ize back-formations are well established and undisputed, such as baptize, memorize, and even prioritize (a relative newcomer whose first usage is from 1961, according to Merriam-Webster [“Prioritize”]). Forgive the pun, but one could say that such –ize back-formations have been normalized.
Back-formations ending in –ify may also be met with an arched eyebrow: consider yuppify, countrify, and frenchify. But, like –ize back-formations, there are plenty of –ify words that don’t strike most of us as dubious: consider beautify, simplify, and personify. Again, among the more accepted ones, some have been in use for centuries, while others, such as gentrify, a back-formation of gentrification, are relatively new in the language (“Gentrify”).
Then there are back-formations that appear to offend because they are presumed to be redundant with a word that already exists. Do we need orientate (from orientation) when we already have orient? What about commentate (from commentator) when we have the verb comment? Or administrate (from administration) when administer does the job?
Whether a back-formation strikes you as perfectly acceptable or possibly iffy or downright wrong is somewhat relative, and opinions will vary. I happen to bristle at the words enthuse (from enthusiasm) and the aforementioned orientate. If you want a more objective opinion beyond your own pet peeves, look in a good dictionary or usage guide. Back-formations may be indicated in the dictionary with the label “back-formation.” You may also learn from the dictionary how old a back-formation is, but remember that the age of a word is not necessarily an indicator of its acceptability. A dictionary may also have usage notes that provide hints: for example, Merriam-Webster tells me that enthuse “has been disapproved since about 1870” but is “flourishing nonetheless . . . especially in journalistic prose” (“Enthuse”). Which brings us to a final point: context matters. In formal writing, such as a research paper, you would be wise to avoid using back-formations that are considered nonstandard, though you may feel more free to use them in informal contexts.
“Enthuse.” Merriam-Webster, 2022, www.merriam-webster.com/dictionary/enthuse.
“Gentrify.” Merriam-Webster, 2022, www.merriam-webster.com/dictionary/gentrify.
“Prioritize.” Merriam-Webster Unabridged, 2022, www.unabridged.merriam-webster.com/collegiate/prioritize.