Ingrammar, anadjectiveis a 'describing' word; the mainsyntacticrole of which is toqualifyanounornoun phrase, giving more information about the object signified.
Adjectives are one of the traditional eightEnglishparts of speech, althoughlinguiststoday distinguish adjectives from words such asdeterminersthat formerly were considered to be adjectives. In this paragraph, "traditional" is an adjective, and in the preceding paragraph, "main" is.