Reibun
。

While you were away from the room, I took the liberty of borrowing the dictionary.

Literal

Room [in-に] exist-not-was [while-間に] without-permission dictionary [object-を] humbly-borrowed.

A keigo-rich sentence: おられない uses the honorific passive おる + られる for 'you were not present,' 勝手に means 'without permission/on my own initiative,' and お借りしました uses the humble お~する pattern. The speaker apologetically admits to borrowing without asking.