infirmus

Infirmus is a Latin adjective meaning weak or feeble, especially in health, and can also be used figuratively to denote a lack of strength or vigor. The word is formed from in- “not” and firmus “firm” or “strong,” yielding the sense “not firm.”

In classical Latin infirmus described people who were ill or frail and appeared in medical, legal, and literary texts. The term carried both physical and moral connotations of weakness. After the fall of the Roman Empire, infirmus continued to be used in ecclesiastical and scholastic Latin, accumulating a set of derivatives that entered English through later Latin and Old French.

The most familiar English descendants are infirm, infirmary, and infirmity, all tied to the core idea of sickness or a lack of strength. In scientific naming, Latin adjectives such as infirmus may appear as species epithets to suggest diminutive size or frailty, though such usage is not standardized and depends on the describer’s intention. Today, infirmus is primarily of historical and linguistic interest, reflected in etymology discussions and in the roots of related English terms rather than as an active technical term in modern scientific or medical practice.