We don't have synonyms for crab-apple yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are crabapple and crab apple.
(n) :
Alternative spelling of crabapple. [Any of the wild species of apple tree, genus Malus, which generally yield small, bitter fruit (in comparison to domestic apples, Malus domestica).]
(n) :
Alternative spelling of crabapple. [Any of the wild species of apple tree, genus Malus, which generally yield small, bitter fruit (in comparison to domestic apples, Malus domestica).]