What does infirm mean?
Infirm is a formal adjective meaning physically weak, frail, or unable to function normally because of illness, old age, or disability. In contemporary use, it most often describes someone who needs substantial care or assistance: an elderly person may be described as old and infirm, while an illness may leave a patient weak and infirm. The word can also be used in legal and administrative language to describe a decision, agreement, or purpose that lacks firm legal standing. An older meaning, referring to mental unsoundness, is now generally avoided because it can be stigmatizing and offensive. Infirm is related to the Latin infirmus, meaning “not strong,” and contrasts with words such as strong, healthy, fit, and sound. Although its vocabulary is useful for precise formal writing, less formal alternatives such as frail, weak, or ailing are often more natural in everyday speech.
Weak or frail in health, especially because of old age or illness.
"The hospital has created a new ward for infirm patients."
Formal and relatively literary; less common in ordinary speech than weak, frail, or ailing.
Lacking firmness, authority, or legal validity.
"The court considered the witness's testimony infirm and gave it little weight."
Common in legal and administrative contexts, especially in the phrase infirm decision or infirm purpose.
From the Latin for “not strong,” infirm has long described both physical frailty and decisions that are legally unstable.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does infirm come from?
The word comes from Latin infirmus, formed from the prefix in-, meaning “not,” and firmus, meaning “strong.” It entered English in the late Middle English period through Old French and Latin usage. Latin derivatives include infirmitas, meaning “weakness,” and infirmarium, the source of English infirmary, a place for the sick. The modern legal senses developed from the idea of something lacking firmness or validity.
Related word forms
How infirm is actually used
The word is formal and relatively literary. In modern use, it most often describes physical weakness or frailty. The sense meaning mentally unsound is now considered dated and may be offensive when applied to a person; legal and administrative uses usually refer to an infirm decision, purpose, or instrument.