An adjective is a root that denotes a property.
"Adjective" is defined here in notional terms, following Haspelmath (2023) (see also this blogpost: https://dlc.hypotheses.org/3467). Many authors define "adjective" also (or alternatively) in terms of coding strategies (e.g. presence of a copula in predicate use, or lack of a relativizer in adnominal use), but languages show substantial differences in their coding strategies.
adjective (CXN) = the head of an attributive phrase that denotes a property. Example: the word new in a very new book is an adjective – it is a property concept that is the head of the attributive phrase very new and modifies book. (Sections 2.2.3, 4.1.1)