From Middle English effectual, effectuel, from Old French effectuel, from Late Latin effectualis.

• IPA: /iˈfɛkt͡ʃuəl/

effectual

1. Producing the intended result; entirely adequate.
   • 1749, [John Cleland], “(Please specify the letter or volume)”, in Memoirs of a Woman of Pleasure [Fanny Hill], London: […] [Thomas Parker] for G. Fenton [i.e., Fenton and Ralph Griffiths] […], →OCLC ↗:

     Redoubling, then, the active energy of his thrusts, favoured by the fervid appetite of my motions, the soft oiled wards can no longer stand so effectual a picklock, but yield, and open him an entrance.

• ineffectual

• effect
• effective
• effectivity
• efficacious

• efficacity
• efficacy
• efficiency
• efficient