Semantic broadening, also called generalization or widening, is the process by which a word's range of reference expands so that it covers more entities, situations, or contexts than it originally did. It is one of the four classical outcomes of semantic change in the Bloomfieldian typology, paired with its inverse, narrowing.
Broadening usually proceeds through a chain of incremental extensions rather than a single leap. A word applied to a specific subtype of a category gradually generalises to the whole category, then sometimes to a broader superordinate. The trigger may be metaphorical similarity, metonymic contiguity, or simple frequency in extended use until the original restriction fades. Generic-trademark drift (Kleenex for any tissue, Hoover for any vacuum, Xerox for any photocopier) is a contemporary instance of broadening in progress.
Broadening produces polysemy as a transitional state: a word may carry both narrow and broad senses simultaneously before the older restricted meaning is lost. Holiday still retains its etymological "holy day" sense in some religious contexts but is dominantly used as "any day off work." Whether a particular case counts as broadening or stable polysemy depends on whether the broader sense has displaced the narrower one as the default.
Broadening and narrowing are not fixed historical destinies. The same lexical field often shows complementary movement: as one term broadens, another narrows to fill the vacated specific niche. Dog broadens; hound narrows. Bird broadens; fowl narrows. Meat narrows from "any food" to "animal flesh"; food broadens from earlier specific senses to take over the general slot. This compensatory pattern reflects the lexicon's tendency to maintain coverage of the relevant conceptual space.
For learners, broadening explains why etymologically transparent compounds sometimes seem semantically opaque (barn contains no audible trace of "barley"; holiday is rarely holy). It also clarifies why archaic-sounding fixed expressions (the powers that be, kith and kin, high time) preserve narrow senses no longer productive in everyday usage.
In vocabulary teaching, awareness of historical broadening supports more nuanced corpus reading. Pre-1700 texts use meat, deer, fowl, brid, hound, and thing in senses that are now archaic, and a learner who knows the diachronic story is less likely to misread early modern literature.