DECREASE, LESSEN, DIMINISH, REDUCE, ABATE, DWINDLE mean to grow or make less.

DECREASE suggests a progressive decline in size, amount, numbers, or intensity.

e.g. slowly decreased the amount of pressure

LESSEN suggests a decline in amount rather than in number.

e.g. has been unable to lessen her debt

DIMINISH emphasizes a perceptible loss and implies its subtraction from a total.

e.g. his visual acuity has diminished

REDUCE implies a bringing down or lowering.

e.g. you must reduce your caloric intake

ABATE implies a reducing of something excessive or oppressive in force or amount.

e.g. the storm abated

DWINDLE implies progressive lessening and is applied to things growing visibly smaller.

e.g. their provisions dwindled slowly

verb no object

diminish gradually in size, amount, or strength:

〈数･量･力などが〉 «…から/…に» だんだん減少［低下］する(away)(decrease) «from/to, into»

e.g. traffic has dwindled to a trickle.

late 16th century: frequentative of Scots and dialect dwine ‘fade away’, from Old English dwīnan, of Germanic origin; related to Middle Dutch dwīnen and Old Norse dvína.