Roughly means more or less, give or take a bit. Roughly ten, roughly speaking, roughly the same.
As a hedge before a number it is the everyday equivalent of approximately, and roughly speaking introduces a simplification. The other sense is about manner: handled roughly, treated roughly — which is physical and usually a complaint. Note rough, roughness; and that a rough guide, a rough draft and a rough idea all use rough in the sense of unfinished rather than harsh.
1adverbroughlyMore or less; give or take a bit.
“The two boxes are roughly the same size, so either will do.”
2adverbharshIn a harsh or violent manner.
“The guard pushed the prisoner roughly into the back of the van.”
roughly is a manner of approximation.
Also accepted in games: approximately, about
Proto-Germanic
*rūhaz
Old English
rūg
Middle English
rough
English
rough
English, today
roughly
From rough + -ly. rough comes from Middle English rough, roughe, roȝe, row, rou, ru, ruȝ, ruh, from Old English rūg, rūh, from Proto-Germanic rūhaz. Cognate with Scots ruch, rouch (“rough”), stq ruuch, rouch (“rough”), West Frisian rûch (“rough”), Low German ruuch (“rough”), Dutch ruig (“rough”), German rau (“rough”), Danish ru (“uneven on the surface, "rough", "rugged"”).
Etymology from Wiktionary, CC BY-SA