Roughly can mean in a way that is not gentle or careful, or it can mean approximately, without being exact. People use it when they only know an estimate, not a precise number.
From *rough* + *-ly*, forming an adverb. The sense of “approximately” developed from the idea of something being not finely or exactly finished.
When you say “roughly 10 minutes,” you’re admitting your number is a bit bumpy, not smooth and precise. It’s a polite way of saying, “Don’t hold me to this exact figure.”
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