mash, quash, strangle, smother, suffocate, envelop, suppress, kill, cover, bury, mute, subdue, extinguish, muffle, engulf, hinder, throttle, stifle, inhibit, disable, stymie, hold down, cramp someone's style, damp, dampen, immobilize

modify, temper, muffle, adjust, modulate (one's voice), slow, moderate, quiet, hush, articulate, intone, vocalize, soften (one's tone), attune, regulate (one's tone), downstep

coo, hiss, hum, sigh, soothe, purr, calm, breathe, whisper, lull, hush, murmur, shush, sweet-talk, croon, quell, talk under one's breath, speak softly, mouth (words)

weigh, wait, tone down, temper, step back, restrain oneself, exercise (restraint), assure, postpone, rephrase, relent, apologize, blunt, redress, allow, compliment, disarm, reassure, settle down, time, commiserate, spare, hear someone out, calm (down/oneself), curb (one's anger/reactivity), dial down/back, acknowledge (a different point of view), agree (with), hear (an opposing view), back off/down, tread (lightly), respect (differences), retract (an inflammatory statement), exercise restraint