descend

angle, cant, cock, heel, incline, lean, list, recline, slant, slope, tilt, tip

abate, de-escalate, diminish, downsize, dwindle, recede, wane

break down, corrupt, decompose, degrade, dilapidate, disintegrate, molder, putrefy

sour, spoil

lessen, lower, reduce

debilitate, undermine

droop, fail, fall, flag, lag, languish, run down, sag, slip, waste (away), weaken, wilt

abate, decrease, de-escalate, die (down), diminish, droop, dwindle, ebb, lessen, let up, moderate, subside, taper off, wane

recede, retreat

deplane, detrain