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1. of extreme force, degree, or strength:

〈熱･圧力･光などが〉強烈な, 猛烈な

e.g. the job demands intense concentration

e.g. the heat was intense

e.g. an intense blue.

(of an action) highly concentrated:

〈感情･行動などが〉(抑えきれないほど)激しい, 極度の, 熱烈な; 懸命の, 集中した

e.g. a phase of intense activity.

2. having or showing strong feelings or opinions; extremely earnest or serious:

｟非難して｠ 〈人が〉感情的になりやすい, ひどくまじめな.

e.g. an intense young woman, passionate about her art

e.g. a burning and intense look.

intenseness | inˈtensnəs | noun

late Middle English: from Old French, or from Latin intensus ‘stretched tightly, strained’, past participle of intendere (see intend).

Intense and intensive are similar in meaning, but they differ in emphasis. Intense tends to relate to subjective responses—emotions and how we feel—while intensive tends to relate to objective descriptions. Thus an intensive course of instruction simply describes the type of course: one that is designed to cover a lot of ground in a short time. On the other hand, in the course was intense, the word intense describes how someone felt about taking the course.