What is the Latin word for inefficacy?

The usual Latin words for “inefficacy” are imbēcillitās, īnfirmitās, parum. The right choice depends on the sense; see the distinctions below.

English → Latin

“inefficacy” in Latin

imbēcillitāsweakness, feebleness; powerlessness, helplessness; illness īnfirmitāsweakness, feebleness, infirmity; sickness parumvery little; insufficient, not enough, too little

Riddle & Arnold A Copious and Critical English–Latin Lexicon, 1864

inefficacy

imbecillitas: infirmitas (weakness); or by circumlocution with parum valere (contra aliquid, if the measures are opposed to something): minus or nihil valere (to have too little or no strength): parvo ad aliquid (or ad aliquid faciendum) momento esse, etc. He complains of the inefficacy of the remedy, *queritur imbecillius esse remedium, quam morbum.

Quick answer

What is the Latin word for inefficacy?: The usual Latin words for “inefficacy” are imbēcillitās, īnfirmitās, parum. The right choice depends on the sense; see the distinctions below.

Entry from J. E. Riddle & T. K. Arnold, A Copious and Critical English–Latin Lexicon (rev. C. Anthon, New York: Harper, 1864), digitised by Fergus J. P. Walsh, CC BY-SA 4.0; Latin markup adapted by latindictionary.co.