Words related to infirm
In Old French and Middle English often en-, but most of these forms have not survived in Modern English, and the few that do (enemy, for instance) no longer are felt as negative. The rule of thumb in English has been to use in- with obviously Latin elements, un- with native or nativized ones.
Proto-Indo-European root meaning "to hold firmly, support."
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit dharmah "custom, statute, law," dharayati "holds;" Prakrit dharaṇa "a holding firm;" Iranian dāra‑ "holding;" Greek thronos "seat;" Latin firmus "strong, steadfast, enduring, stable;" Lithuanian diržnas "strong;" Welsh dir "hard," Breton dir "steel."
late 14c., infirmite, "disease, sickness; lack of capability, weakness," from Old French infirmité, enfermete "illness, sickness, disease; moral weakness," and directly from Latin infirmitatem (nominative infirmitas) "want of strength, weakness, feebleness," also "the weaker sex" [Lewis], noun of quality from infirmus "weak, frail" (see infirm).