1. (v. t.) To make weak; to lessen the strength of; to deprive of strength; to debilitate; to enfeeble; to enervate; as, to weaken the body or the mind; to weaken the hands of a magistrate; to weaken the force of an objection or an argument.

2. (v. t.) To reduce in quality, strength, or spirit; as, to weaken tea; to weaken any solution or decoction.

3. (v. i.) To become weak or weaker; to lose strength, spirit, or determination; to become less positive or resolute; as, the patient weakened; the witness weakened on cross-examination.

abate afflict aggravate allay alleviate assuage attemper attenuate bank the fire bate beat blunt break bugger burn out cave in chasten collapse come apart come unstuck conk out constrain control cramp cripple crumble cut damage damp dampen de-emphasize de-energize deaden debilitate decline dematerialize derange deteriorate devitalize dilapidate dilute diminish disable disedge disembody disenable disintegrate disorder do in do up downplay drain draw the teeth droop drop dull dwindle ease emacerate emaciate emasculate embitter endamage enervate enfeeble etherealize eviscerate exacerbate exhaust extenuate fade fag fag out fail faint fall short fatigue fizzle out flag frazzle give out give way go downhill go soft go to pieces gruel hamstring harass harm hit the skids honeycomb hors de combat hospitalize hurt impair inactivate incapacitate indispose injure invalid irritate jade keep within bounds kibosh knock out knock up lame languish lay lay low lay up lenify lessen lighten lose strength maim make worse minimize mitigate moderate modulate obtund overfatigue overset overstrain overthrow overtire overturn overweary palliate paralyze peak peg out peter out pine play down poop poop out prostrate put put back queer queer the works rarefy rattle reduce reduce the temperature remit repress restrain retund run down sabotage sap sap the foundations shake shake up shrink sicken sink slacken slow down smother sober sober down soften soften up spike spiritualize stifle subdue subtilize subvert suppress tame temper thin thin away thin down thin out throw down throw over tire tire out tire to death tone down tucker tune down turn unbrace undermine underplay unfit unman unnerve unstrengthen unstring upend upset use up wane waste waste away water water down wear wear away wear down wear on wear out wear thin weary wilt wind wing wither wither away worsen wreck yield