See also: chain case English Close-up of a touring bicycle's chaincase Etymology From chain + case. Noun chaincase (plural chaincases) A guard which fits around the chain of a bicycle to protect it from dirt and other environmental hazards, and to protect operators from dirt and danger of trapping. Synonym: chain guard Translations guard around the chain of a bicycle German: Kettenkasten m Wikiwand - on Seamless Wikipedia browsing. On steroids.