Requiring or involving great effort; demanding much mental or physical work.
From effort + -ful suffix. 'Effort' comes from Old French from Latin ex- (out) + fortis (strong), meaning to exert strength. The -ful suffix makes it an adjective describing the quality of requiring effort.
Interestingly, we say things are 'effortless' when they're easy, but 'effortful' sounds awkward even though it's grammatically sound—our brains prefer the negative form to describe the absence of ease.
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