sudden infant death syndrome

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

• noun A fatal syndrome that affects sleeping infants under a year old, characterized by a sudden cessation of breathing and thought to be caused by a defect in the central nervous system.

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

• noun pathology The sudden and unexplained death of an infant aged one month to one year, normally while sleeping.

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

• noun sudden and unexpected death of an apparently healthy infant during sleep