아주 is technically rather closer to extremely despite how it sounds. Here's an excerpt from the tips and notes:
There are various words used to give emphasis, like very in English. Here we are introducing a couple of them.
|매우, 아주, 굉장히||very, so, greatly, highly, exceedingly|
|정말(로), 진짜(로), 참(으로)||really, truly, indeed, (non-standard) very, so|
|특히||in particular, particularly, especially, specially|
|상당히||considerably, fairly, rather, quite|
|꽤||quite, fairly, rather, pretty|
|엄청||overly, too, excessively, awfully|
|너무||too, overly, excessively, awfully, so Read more|
There aren't really one-to-one translations for these, so here we accept what's listed above.