Thorough means complete and careful, paying attention to all the details and making sure nothing gets overlooked. When you do something in a thorough way, you check your work and finish the job properly.

A thorough cleaning of your room means dusting shelves, organizing drawers, vacuuming corners, and really finishing the job (not just shoving things under your bed!). A thorough investigation by a detective involves examining every clue, interviewing every witness, and following every lead until the mystery is solved.

Being thorough takes extra time and effort, but it prevents problems later. A builder who does thorough work measures twice, checks that everything is level and secure, and tests that doors and windows open smoothly. A student who writes a thorough book report discusses the plot, characters, themes, and what made the story meaningful.

The opposite of thorough is careless or hasty. When someone does a sloppy job, they rush through and miss important steps. When they're thorough, they stick with the task until it's truly done right. You might hear someone praised for being thorough in their research, their planning, or their preparation because it shows they take their work seriously.