Definitions for crab apple
Random House Webster's College Dictionary
any of various small, tart, cultivated or wild varieties of apple, used for making jelly and preserves.
any tree bearing such fruit.
Origin of crab apple:
crab apple, crabapple, cultivated crab apple(noun)
any of numerous varieties of crab apples cultivated for their small acidic (usually bright red) fruit used for preserves or as ornamentals for their blossoms
wild apple, crab apple, crabapple(noun)
any of numerous wild apple trees usually with small acidic fruit
crab apple, crabapple(noun)
small sour apple; suitable for preserving
"crabapples make a tangy jelly"