feeble or weak in body or health, especially because of age; ailing.
unsteadfast, faltering, or irresolute, as persons or the mind; vacillating: infirm of purpose.
not firm, solid, or strong: an infirm support.
unsound or invalid, as an argument or a property title.

verb (used with object)

to invalidate.

Origin of infirm

1325–75; Middle English infirme < Latin infirmus. See in-3, firm1
Related formsin·firm·ly, adverbin·firm·ness, noun

Synonyms for infirm

1, 3, 4. weak. 2. wavering, indecisive. 3. rickety, tottering, shaky, unsteady.

Antonyms for infirm

1–3. strong. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for infirm

Contemporary Examples of infirm

Historical Examples of infirm

British Dictionary definitions for infirm



  1. weak in health or body, esp from old age
  2. (as collective noun; preceded by the)the infirm
lacking moral certainty; indecisive or irresolute
not stable, sound, or securean infirm structure; an infirm claim
law (of a law, custom, etc) lacking legal force; invalid
Derived Formsinfirmly, adverbinfirmness, noun
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for infirm

late 14c., "weak, unsound" (of things), from Latin infirmus "weak, frail, feeble" (figuratively "superstitious, pusillanimous, inconstant"), from in- "not, opposite of" (see in- (1)) + firmus (see firm (adj.)). Of persons, "not strong, unhealthy," first recorded c.1600. As a noun from 1711.

Online Etymology Dictionary, © 2010 Douglas Harper

infirm in Medicine




Weak in body, especially from old age or disease; feeble.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.