concentrated on a single subject or into a short time; very thorough or vigorous

she undertook an intensive Arabic course

eight days of intensive arms talks

(of an adjective, adverb, or particle) giving force or emphasis

denoting a property which is measured in terms of intensity (e.g. concentration) rather than of extent (e.g. volume), and so is not simply increased by addition of one thing to another

an intensive adjective, adverb, or particle; an intensifier