"A Real Gem"
Crummy means shabby, miserable, or of little value. The word was originally spelled crumby, but crumby is shedding that definition and is increasingly confined to its older senses—(1) full of or covered in crumbs, and (2) tending to break into crumbs. In the second sense, it’s synonymous with crumbly.
Crumby has been in English since the 17th century, and it gained the slang senses now associated with crummy in the 19th century. Crummy has several little-used old definitions, but it emerged as a newer spelling of crumby in its slang senses only in the second half of the 20th century. Crumby still appears in place of crummy much more often than the reverse, but the differentiation is fairly well established this century and is in evidence in newswriting and books from around the English-speaking world.
Still, the words will probably remain variants of each other because they are so closely related—both come from crumb —and because neither is very common, meaning people don’t encounter them enough to feel certain of how they’re spelled.
