drag, sag, die, age, fade, wane, die down, peter out, ebb, subside, sputter, weaken, melt, lapse, decline, teeter, wither, flag, fizzle out, fade away/out, abate, wind down, tire, lose ground, waste away, wilt, burn out, grow old, lose steam, taper off, gutter

hollow out, squash, quash, thin, water down, beat down, weaken, endanger, jeopardize, encumber, impair, undermine, sap, suck out, incapacitate, exhaust, erode, blunt, drain (of vitality), enervate, starve, grind down, tax (one's reserves), hit someone hard, wind (one from exertion), tire someone out, debilitate, fatigue, wear out/down, devitalize, eat away, chip away at, weary, defang

cushion, mute, absorb, dull, muffle, silence, blunt, dampen, deaden, quiet, buffer, soundproof, create a sound barrier