(By Leon Stassen:) "This map shows the distribution of the various options in the encoding of predicative adjectives, i.e. items which predicate a property of a subject. The basic distinction is between those languages in which predicative adjectives are encoded in a way that is parallel to predicative verbs, and those languages in which the encoding of predicative adjectives and verbs is different. An example of this latter, nonverbal, encoding of predicative adjectives is English..., [which] shows third person agreement in the present tense of its predicative verbs, but this option is not available for predicative adjectives: *John tall-s is not acceptable in the language. On the other hand, Bororo (Macro-Gê; Mato Grosso, Brazil) offers an instance of verbal encoding of predicative adjectives; ... [where] the encoding of predicative verbs and of predicative “property words” is identical."
In Stassen's WALS feature, "adjective" is understood as "property-denoting word" ("an item which predicates a property of a subject"), independently of the strategy for encoding. This is very similar to the Grammaticon's definition of "adjective".