painful toil: the strenuous, grinding labor that wears down the body and weighs on the heart, the kind of effort that the curse made the human lot
This is a rare and weighty word. It names not a sharp, momentary pain but the long, hard effort that a person sweats and aches through over a lifetime. The shape of the word in Hebrew is the kind used for a settled state or condition, so it points to a standing burden rather than a single hurt: the wearing struggle to get a living and to raise a family in a broken world.
It appears only three times, and all three sit inside one story, the curse that follows the first wrong in the garden. To the woman it is the hardship bound up with bearing and raising children; to the man it is the back-breaking work of forcing food from ground that now fights him; and when Lamech names his son Noah, he reaches back to the very same word, longing for relief from the toil of his hands on the cursed soil. The writer chose this uncommon word on purpose, so that the reader would hear the man's burden, the woman's burden, and Lamech's hope as one connected chain.
Because the word leans toward effort that grieves as much as it tires, English Bibles have pulled it in two directions, sometimes toward sorrow and pain, sometimes toward toil and labor. Both poles are really in the word: it is hard work that hurts. The most careful sense holds the two together, painful toil or strenuous hardship, the daily grind that exhausts the body and saddens the spirit.