To do something intensively means to do it with great concentration, effort, and focus over a relatively short period of time. When you study intensively for a spelling bee, you might spend several hours each day drilling words, writing them out, and testing yourself, rather than glancing at the word list once a week.

The word emphasizes both the strength of effort and the concentrated nature of that effort. An athlete training intensively before a championship doesn't just practice more: they focus deeply on specific skills, pushing themselves hard during dedicated training sessions. A scientist might research a problem intensively for three months, working long hours and thinking about little else.

Intensive often appears in phrases like “intensive care unit” (where doctors and nurses monitor patients very closely) or “intensive course” (where you learn a lot in a short time, like a two-week intensive Spanish class that covers a whole semester's material).

The opposite approach would be doing something casually or sporadically: glancing at your math homework occasionally versus sitting down and working through problems intensively for an hour. When you work intensively, you're all in, giving something your full attention and energy for that time.