To increase; to grow (in amount, degree, intensity). Used for quantities, feelings, effects, etc.; can be intransitive or causative in context.
寒さが増してきたのでコートを出した。
The cold has increased, so I took out my coat.
経験を積むにつれて自信が増す。
As you gain experience, your confidence increases.
不安は時間とともに増す一方だった。
The anxiety only grew with time.
適切な栄養を与えれば作物の収量は増すだろう。
If you provide proper nutrition, the crop yield will likely increase.