Something that requires a lot of hard work, effort, or time to complete; tedious and tiring.
From Latin 'laboriosus' (from 'labor' meaning work). Used in English since the 1500s to describe heavy, exhausting tasks.
Before computers, writing manuscripts was so laborious that monks in medieval monasteries spent entire lifespans copying books—one mistake near the end meant starting over, which is why some added funny margin notes as they slowly lost their minds.
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