noun

1. a very small piece broken off something; small particle or bit, esp. of bread, cake, etc.
2. any bit or scrap crumbs of knowledge
3. the soft part of bread within the crust
4. ☆ Slang a worthless, disgusting, or despicable person
   also crumbum crum′·bum′

Etymology: ME crome < OE cruma, lit., scraping from bread crust, akin to Ger krume < IE *gr-eu, to scratch, scrape (> Ger krauen, to scratch) < base *ger-, to turn, twist

transitive verb

1. Rare to crumble
2. to clear of crumbs to crumb a table
3. Cooking to cover or thicken with crumbs