defficacious 

Adjective: Successful in producing a shitty results; ineffective.

Contrast with "efficacious".

The medicine was defficacious; My cough only worsened after taking it.

His defficacious work resulted in extended work hours for all his co-workers.

defficacious by efficacious_eruditer October 20, 2012

efficacious 

A douchey way of saying effective.

When trying to impress with his vocabulary by using the word 'efficacious' rather than 'effective', the man was actually more efficacious at sounding like an ass.

efficacious by dgeezy May 13, 2015

defecacious 

Having the ability to find a good, clean place to take a shit, by instinct alone. A portmanteau word from "DEFEcate + effiCACIOUS.

I don't know how George found that nice, clean rest stop five miles down the highway---he's very defecacious!

defecacious by pentozali September 9, 2012

efficacious 

An adjective (descriptive word):

Describing thing, or person, producing, or sure to produce, desired effect.

"Efficaciously" (adverb) describing the behaviour of act in such a manner as to effect the desired effect.
I may help to understand that the Latin root for these words is the same as that for "Efficient".

Asprin is truly "efficacious" for the treatment of headaches.

I've never known a teacher to be so consistent in dealing so "efficaciously" with problem students, as he does.

efficacious by Sparticus774 May 27, 2014