To weaken is to become less powerful or strong. When a storm weakens, the wind dies down and the torrential rain becomes a light drizzle.

If you weaken physically, your strength diminishes: "I did great at the start of the obstacle course, but my arms began to weaken toward the end and I couldn't climb that last wall." You can also weaken in resolve or spirit, like when your sister's criticism of your art project weakens your confidence about including it in an exhibition. This verb comes from weak and its Germanic root meaning "yield" or "soft."

Definitions of weaken
  1. verb
    lessen the strength of
    “The fever weakened his body”
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    beef up, fortify, strengthen
    make strong or stronger
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    de-energise, de-energize
    deprive of energy
    weaken or destroy in spirit or body
    devitalise, devitalize
    sap of life or energy
    undermine or cause to waver
    lessen the activity or force of
    remove a brace or braces from
    make weak by stunting the growth or development of
    cripple, stultify
    deprive of strength or efficiency; make useless or worthless
    cut, dilute, reduce, thin, thin out
    lessen the strength or flavor of a solution or mixture
    attenuate, rarefy
    weaken the consistency of (a chemical substance)
    make less intense
    mollify, season, temper
    make more temperate, acceptable, or suitable by adding something else; moderate
    debilitate, drain, enfeeble
    make weak
    weaken physically, mentally, or morally
    reduce the amplitude (of oscillations or waves)
    negate, neutralise, neutralize, nullify
    make ineffective by counterbalancing the effect of
    castrate, emasculate
    deprive of strength or vigor
    wash out
    deplete of strength or vitality
    take away a vital or essential part of
    emaciate, macerate, waste
    cause to grow thin or weak
    water down
    make less strong or intense
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    alter, change, modify
    cause to change; make different; cause a transformation
  2. verb
    reduce the level or intensity or size or scope of
    synonyms: de-escalate, step down
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    escalate, intensify, step up
    increase in extent or intensity
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    decrease, lessen, minify
    make smaller
  3. verb
    lessen in force or effect
    synonyms: break, damp, dampen, dilute, soften
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    make soundproof
    damp, dampen, deaden
    make vague or obscure or make (an image) less visible
    type of:
    blunt, deaden
    make less lively, intense, or vigorous; impair in vigor, force, activity, or sensation
  4. verb
    become weaker
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    gain strength
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    become weaker, in strength, value, or magnitude
    disappear, evaporate, melt
    become less intense and fade away gradually
    die down
    become progressively weaker
    lose significance, effectiveness, or value
    fade, melt
    become less clearly visible or distinguishable; disappear gradually or seemingly
    lessen, subside
    wear off or die down
    blur, dim, slur
    become vague or indistinct
    languish, pine away, waste
    lose vigor, health, or flesh, as through grief
    make less lively or vigorous
    lose strength or effectiveness; become or appear boring, insipid, or tiresome (to)
    loose, loosen, relax
    become loose or looser or less tight
    become looser or slack
    slack, slacken, slow, slow down, slow up
    become slow or slower
    lose strength
    efface, obliterate
    remove completely from recognition or memory
    make milky or dull
    attenuate or reduce in vigor, strength, or validity by polishing or purifying
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    decrease, diminish, fall, lessen
    decrease in size, extent, or range
  5. verb
    destroy property or hinder normal operations
    synonyms: counteract, countermine, sabotage, subvert, undermine
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    cause to run off the tracks
    type of:
    refuse to go along with; refuse to follow; be disobedient
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