is a specific kind of: alter, change, modify.

is a broader term that covers: suppress | mitigate | pare, pare down | circumscribe, confine to, limit | boil down, concentrate, reduce | reduce, shrink | abbreviate, abridge, contract, cut, foreshorten, reduce, shorten | abate, slack, slake | lour, lower, turn down | de-escalate, step down, weaken | minimise, minimize | bring down, cut, cut back, cut down, reduce, trim, trim back, trim down | cut | relax, slack, slack up, slacken | belittle, diminish ... show more.

is the opposite of: increase.

derivation: decrease, drop-off, lessening.