Mawson, C.O.S., ed. (1870–1938). Roget’s International Thesaurus. 1922.

Class I. Words Expressing Abstract Relations
Section VIII. Causation
2. Connection Between Cause and Effect

160. Weakness.

   NOUN:WEAKNESS &c. adj.; debility, atony, relaxation, languor, enervation; impotence [See Impotence]; infirmity, effeminacy, feminality; fragility, flaccidity; inactivity [See Inactivity].
  [COMPARISONS] reed, thread, rope of sand, house of cards, house built on sand.
  ANÆMIA, bloodlessness, deficiency of blood, poverty of blood.
  INVALIDATION; declension -, loss -, failure- of strength; delicacy, decrepitude, asthenia, adynamy [rare], cachexia or cachexy, sprain, strain.
  WEAKLING; softling [obs.]; infant [See Infant]; youth [See Youth].
   VERB:BE WEAK &c. adj.; drop, crumble, give way, totter, dodder, tremble, shake, halt, limp, fade, languish, decline, flag, fail, have one foot in the grave.
  RENDER WEAK &c. adj.; weaken, enfeeble, debilitate, invalidate, shake, deprive of strength, relax, enervate; unbrace, unnerve; cripple, unman &c. (render powerless) [See Impotence]; cramp, reduce, sprain, strain, blunt the edge of; dilute, impoverish; decimate; extenuate; reduce in strength, reduce the strength of; mettre de l’eau dans son vin [F.].
   ADJECTIVE:WEAK, feeble, debile [obs.]; impotent [See Impotence]; relaxed, unnerved &c. v.; sapless, strengthless, powerless; weakly, unstrung, flaccid, adynamic, asthenic; nervous.
  SOFT, effeminate, feminate [obs.], womanish.
  FRAIL, fragile, shattery; flimsy, sleazy, gossamery, papery, unsubstantial, gimcrack, gingerbread; rickety, jerry-built, kucha or kachcha [Hind.], cranky; craichy [dial. Eng.], drooping, tottering, doddering [colloq.] &c. v.; broken, lame, withered, shattered, shaken, crazy, shaky, tumbledown; palsied [See Impotence]; decrepit.
  UNSOUND, poor, infirm; faint, faintish; sickly (disease) [See Disease]; dull, slack, evanid [obs.], languid; spent, shortwinded, effete; weather-beaten; decayed, rotten, forworn [archaic], worn, seedy, languishing, wasted, washy, wishy-washy [colloq.], laid low, pulled down, the worse for wear.
  UNSTRENGTHENED [See Strength], unsupported, unaided, unassisted; aidless, defenseless [See Impotence].
  on its last legs; weak as a -child, – baby, – chicken, – cat, – rat, – rag; weak as -water, – water gruel, – ginger-bread, – milk and water; colorless [See Achromatism].
  1. Non sum qualis eram.
  2. At the hour when sick men mostly die and sentries on lonely ramparts stand to their arms.—Dunsany
  3. To be weak is miserable, Doing or suffering.—Milton