(n.) A word used as the designation or appellation of a creature or thing, existing in fact or in thought; a substantive.

abstract noun adherent noun air atom atomic particles axiom brute matter building block center chemical element collective noun common noun component constituent core earth element elementary particle elementary unit elixir essence essential fire flower focus fundamental fundamental particle gerund gist gravamen heart hyle inner essence kernel marrow material material world materiality matter meat molecule monad natural world nature nominal noun noun phrase nub nucleus nuts and bolts physical world pith plenum postulate principle pronoun proper noun quid quiddity quintessence quotation noun sap soul spirit stuff substance substantive substratum the four elements the nitty-gritty unit of being water