The word "whatnot" originated in the mid-16th century as a direct combination of the interrogative pronoun "what" and the adverb "not," forming the phrase "and what not?" meaning "and anything else?" or "and other such things." This phrase functioned as an indefinite extension of a list. By the early 19th century, the phrase had fused into a single lexical item, solidifying its modern pronominal meaning. The noun sense, referring to a piece of furniture for displaying miscellaneous curiosities, emerged in the early 19th century, directly derived from the pronoun's sense of "miscellaneous unspecified items," as such shelves were designed to hold an assortment of ornaments and knick-knacks.

The word is a lexicalized compound formed from the phrase "what not". It functions as a single, indivisible unit in modern English.