Roughly comes from the adjective rough, which dates back to before 1000 and comes from the Old English word rūh. It is similar to Dutch word ruig and the German word rauh. It was first used as an adjective around the year 1300, but it only became a synonym of approximately in the mid-19th century.

What is the origin of the word rough?

Old English ruh "rough, coarse (of cloth); hairy, shaggy; untrimmed, uncultivated," from West Germanic *rukhwaz "shaggy, hairy, rough" (source also of Middle Dutch ruuch, Dutch ruig, Old High German ruher, German rauh), from Proto-Germanic *rukhaz, which is perhaps related to the source of Sanskrit ruksah "rough;" ...

Is roughly a real word?

roughly adverb (NOT EXACTLY)

approximately: There has been an increase of roughly 2.25 million. Roughly speaking, it's 2.25 million.