efficio

Efficio, efficere, effeci, effectum, third conjugation in -io, from ex plus facio: to work a thing out to the finish. With a plain accusative it means to produce or accomplish. With ut and the subjunctive it means to bring it about that something happens, and in argument and chronicle that construction is much the commonest. Logicians use the passive for what a proof establishes, so efficitur often reads best as "it follows".

The neighbours are the trap. Afficio is to affect, conficio to finish off or exhaust, deficio to fail, perficio to complete, interficio to kill. The stem tells you almost nothing and the prefix does all the work, so learn them as separate verbs. English takes effect, effective, efficient and efficacious from the supine stem.