A nominal is an °expression that °can occur on its own and that can serve as an °argument or as an an °adpossessive modifier.
Nominals are often called "nominal phrases" or "NPs" (or "DPs"), but it is not clear how nominals could be defined as kinds of "phrases" (because "phrase" is an abstract notion that is hardly suitable as a comparative concept). ❡
Nominals could also be defined as "object-denoting referring phrases", as in Croft (2022).
nominal phrase (CXN) = a referring phrase whose head denotes an object concept. Example: a large balloon is a nominal phrase; the head balloon denotes an object concept. A nominal phrase is the prototypical referring phrase, and its head is a noun. (Section 2.2.3)