Whatness is a philosophical calque of Latin quidditas ('whatness, essence'), formed from the interrogative what + -ness, rendering the Scholastic concept of a thing's essential nature. In current use it is a noun meaning "the essential nature of a thing; its quiddity or whatness". That sense is explained by the older material without requiring a speculative semantic step: the inherited or borrowed base supplies the field of meaning, while the English formation fixes its modern role. The suffix -ness turns a quality into a noun of state, condition, or degree. The surface form is compositional: its joined elements remain visible in the modern word. A central historical form is Old English hwæt. Related English forms include what and whatever. The word's history is thus visible in its construction: the components remain interpretable even after the whole expression has settled into a conventional English meaning.