effectual

Effectual means good at achieving the results you want. The most effectual method for avoiding cavities? Brush, floss, lay off the candy, and see your dentist every 6 months.

Wait, aren't effectual and effective basically the same adjectives with the same meaning? Well, generally speaking, yes. But if you want to get really nit-picky, you might note that effectual actually describes something that produces the desired result, but in a big way. Effective simply gets the job done. No one is going to call you out for using either word interchangeably though, as long as it's done effectually.

Definitions of effectual
1

adj producing or capable of producing an intended result or having a striking effect

“his complaint proved to be effectual in bringing action”
Synonyms:
effective, efficacious
hard-hitting, trenchant
characterized by or full of force and vigor
impelling
markedly effective as if by emotional pressure
impressive, telling
producing a strong effect
rough-and-ready
crude but effective for the purpose at hand
efficacious
marked by qualities giving the power to produce an intended effect
efficient
being effective without wasting time or effort or expense
potent, stiff, strong
having a strong physiological or chemical effect
powerful
having great power or force or potency or effect
useful, utile
being of use or service
Antonyms:
ineffective, ineffectual, uneffective
not producing an intended effect
idle
not in action or at work
toothless
lacking necessary force for effectiveness
unproductive
not producing desired results
inefficacious
lacking the power to produce a desired effect
inefficient
not producing desired results; wasteful
powerless
lacking power
useless
having no beneficial use or incapable of functioning usefully
show more antonyms...

adj having legal efficacy or force

Synonyms:
legal, sound
valid
well grounded in logic or truth or having legal force