In etymology, back-formation is the process of creating a new lexeme, usually by removing actual or supposed affixes. The resulting neologism is called a back-formation, a term coined by James Murray in 1889. (OED online first definition of 'back formation' is from the definition of to burgle, which was first published in 1889.)
Back-formation is different from clipping – back-formation may change the part of speech or the word's meaning, whereas clipping creates shortened words from longer words, but does not change the part of speech or the meaning of the word.
For example, the noun resurrection was borrowed from Latin, and the verb resurrect was then backformed hundreds of years later from it by removing the ion suffix. This segmentation of resurrection into resurrect + ion was possible because English had examples of Latinate words in the form of verb and verb+-ion pairs, such as opine/opinion. These became the pattern for many more such pairs, where a verb derived from a Latin supine stem and a noun ending in ion entered the language together, such as insert/insertion, project/projection, etc.