drought

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A long period of abnormally low rainfall, especially one that adversely affects growing or living conditions.
• noun A prolonged dearth or shortage.

from The Century Dictionary.

• noun A dialectal form of draft, draught.
• noun Dryness.
• noun Dry weather; want of rain or of moisture; such a continuance of dry weather as injuriously affects vegetation; aridness.
• noun Thirst; want of drink.
• noun Figuratively, scarcity; lack.

from the GNU version of the Collaborative International Dictionary of English.

• noun Dryness; want of rain or of water; especially, such dryness of the weather as affects the earth, and prevents the growth of plants; aridity.
• noun Thirst; want of drink.
• noun Scarcity; lack.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A period of below average rain fall, longer and more severe than a dry spell
• noun by extension, informal A longer than expected term without success, particularly in sport.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a prolonged shortage
• noun a shortage of rainfall