In etymology, back-formation is the process of creating a new lexeme by removing actual or supposed affixes. The resulting neologism is called a back-formation, a term coined by James Murray in 1889. (OED online preserves its first use of 'back-formation' from 1889 in the definition of to burgle; from burglar.)
For example, the noun resurrection was borrowed from Latin, and the verb resurrect was then back-formed 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.