In linguistics, it's called rebracketing:
https://en.wikipedia.org/wiki/Rebracketing
> Rebracketing often focuses on highly probable word boundaries: "a noodle" might become "an oodle", since "an oodle" sounds just as grammatically correct as "a noodle", and likewise "an eagle" might become "a neagle", but "the bowl" would not become "th ebowl" and "a kite" would not become "ak ite".
> Technically, bracketing is the process of breaking an utterance into its constituent parts. The term is akin to parsing for larger sentences, but it is normally restricted to morphological processes at the sublexical level, i.e. within the particular word or lexeme. For example, the word uneventful is conventionally bracketed as [un+[event+ful]], and the bracketing [[un+event]+ful] leads to completely different semantics. Re-bracketing is the process of seeing the same word as a different morphological decomposition, especially where the new etymology becomes the conventional norm. The name false splitting, also called misdivision, in particular is often reserved for the case where two words mix but still remain two words (as in the "noodle" and "eagle" examples above).
Other examples:
> The English word outrage is a loanword from French, where it was formed by combining the adverb outre (meaning "beyond") with the suffix -age; thus, the original literal meaning is "beyondness" – that is, beyond what is acceptable. The rebracketing as a compound of out- with the noun or verb rage has led to both a different pronunciation than the one to be expected for such a loanword (compare umbrage) and an additional meaning of "angry reaction" not present in French.
> Many words coined in a scientific context as neologisms are formed with suffixes arising from rebracketing existing terms. One example is the suffix -ol used to name alcohols, such as methanol. Its origin is the rebracketing of al•cohol as alcoh•ol. The word alcohol derives from the Arabic al-kuḥl, in which al is the definite article and kuḥl (i.e., kohl), is based on the Semitic triliteral root K-Ḥ-L.