slog
v.v. to work very hard for a long time on something difficult. You use this when you feel like the work is slow and boring, but you have to keep going.
v. to work or progress with great effort and difficulty over a prolonged period. Often implies a sense of tedium or physical exhaustion.
I had to slog through the final report all weekend.
The team had to slog through the heavy rain to finish the construction before the storm hit.
After months of slogging through the dense legal documents, the junior partner finally found the loophole that would save the firm from the lawsuit.
Probably a variation of slug (“to hit very hard”) or slough. Possibly related to slag, seen in the North Germanic languages, in association with the third verb and second noun definition.