"less common" is a bit of an understatement[0]. I'd put it in the "common misspelling" category. Though both versions seem to have been around since before En

"less common" is a bit of an understatement[0]. I'd put it in the "common misspelling" category. Though both versions seem to have been around since before English really had consistent spelling. [0] https://books.google.com/ngrams/graph?content=adaption%2Cadaptation&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cadaption%3B%2Cc0%3B.t1%3B%2Cadaptation%3B%2Cc0#t1%3B%2Cadaption%3B%2Cc0%3B.t1%3B%2Cadaptation%3B%2Cc0 https://books.google.com/ngrams/graph?content=adaption%2Cada...