Adjectival

A cover term for a single adjective or a word group with an adjective as a head.

A word or phrase that functions as an adjective to modify a noun.

Examples 

R.L. Trask: "In the following examples, the bold italic item is adjectival: my new book (an adjective phrase consisting only of an adjective); a very long opera (an adjective phrase containing a degree modifier and an adjective); the roses in your garden (a prepositional phrase); a copper-producing region (a participial phrase); his damn-your-eyes attitude (an entire sentence reduced to a modifier); the woman you were talking to (a relative clause). A few linguists would also apply the label adjectival to a noun modifying another noun, as in a security van and a plastic cup, but this use is not normal."

Carl Bache: "Adjectivals typically have one of the following functions:

DEP [dependents] The clever girls told their anxious mother nothing.
Cs [subject complement] Jane is exceptionally intelligent.
Co [object complement] They drove him mad.

Naturally, adjectivals also function as conjoints in compound units, e.g.:

CJT [conjoint] She sent him a long and rather boring letter.

Adjectivals are often used as complements in verbless adverbial clauses:

Cs If necessary, I can help her.
However disagreeable their presence, you have to let them in.

Adjectives serving as dependents in (pro)noun groups are called attributive adjectives while adjectives with subject or object complement function are called predicative adjectives.

"In addition to attributive and predicative uses, adjectivals may assume adverbial function:

A [adverbial] Unhappy with the result, he decided to resign.
Dicky hurried in breathless, wearing his new trenchcoat.
Expressionless he drew his head back in again.

Adjectivals in this last category are sometimes referred to as 'independent' or 'free' complements rather than adverbials."

The Nouny-Verby Split

Harrie Wetzer: "[T]he grammatical behaviour of property concept words, irrespective of their alleged word class status, can be characterized by two opposing tendencies. Adjectivals tend to associate with the nouns or with the verbs; at the same time, they typically display grammatical properties not shared by 'core' nouns or verbs... As opposed to the standardly accepted tripartite division into Adjectives, (adjectival) Nouns, and (adjectival) Verbs, this alternative perspective implies a dichotomy between two groups of adjectivals, which, following Ross (1972, 1973), may be called nouny and verby adjectivals. In this view, the cross-linguistic category 'Adjective' is split up so as to be distributed among the categories of (adjectival) Nouns and (adjectival) Verbs, respectively. Noun-like adjectives, together with (adjectival) nouns, will then constitute the category of 'nouny' adjectivals; the category of 'verby' adjectivals is made up verb-like adjectives and (adjectival) verbs."

Pronunciation: adj-ik-TIE-vel