diminutive formation, from Old French -ette (fem.), used indiscriminately in Old French with masculine form -et. As a general rule, older words borrowed from French have -et in English, while ones taken in since 17c. have -ette. In use with native words since 20c., especially among persons who coin new product names, who tend to give it a sense of "imitation." Also in words like sermonette, which, OED remarks, "can scarcely be said to be in good use, though often met with in newspapers."