flat
1. For still wine, flat describes a dull flavor and character due to a lack of acidity. 2. A sparkling wine sans bubbles is flat.
The New Wine Lovers Companion, 2nd Edition, by Ron Herbst and Sharon Tyler Herbst. Copyright © (1) 2003, 1995 by Ron Herbst and Sharon Tyler Herbst. Reprinted by arrangement with Barron's Educational Series, Inc.