rapid (e.g. progress)
Example sentences
彼が急速に日本語を習得するので私は嬉しかった。
I was pleased with the rapidity with which he mastered Japanese.
発展途上国の人口増加は急速だ。
The growth in population is very rapid in developing countries.
日本経済は急速に成長した。
The Japanese economy developed rapidly.