adjective

1. increasing or causing to increase in degree or amount
2. of or characterized by intensity; thorough, profound, and intense; concentrated or exhaustive
3. designating care of an especially attentive nature given to critically ill hospital patients, typically in a special ward (intensive care unit)
4. Agric. designating a system of farming which aims at the increase of yield per acre by using increased labor, capital, etc.
5. Gram. giving force or emphasis; emphasizing “very” in “the very same man” is an intensive adverb

Etymology: ML intensious < L intensus: see intense & -ive

noun

1. anything that intensifies
2. an intensive word, prefix, etc.