from The American Heritage® Dictionary of the English Language, 4th Edition
- adv. To an extent deserving of regret: a regrettably brief career.
- adv. As a matter of regret: Regrettably, the book is not available.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adv. In a manner inspiring or deserving regret.
from The Century Dictionary and Cyclopedia
- With regret; regretfully.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adv. by bad luck
regrettable + -ly (Wiktionary)