beetle
Synonym discussion
Sense: noun/1
For noun/1, beetle names one particular kind of insect, usually one with a hard back that covers its wings. Insect is the broad scientific and everyday category word, so every beetle is an insect, but not every insect is a beetle. Bug is a very general informal word that people often use for almost any small crawling insect, even when it is not exact. Cockroach names a different insect and often suggests a household pest, so it should not replace beetle unless that is the insect you mean. Say A black beetle crawled under the flowerpot, but A cockroach ran across the kitchen floor.
Etymology
Beetle goes back to Old English bitela, and it is probably related to an older Germanic word meaning bite. The insect was likely given this name because of its biting mouthparts. Much later, Beetle also became the name of the rounded Volkswagen car because people thought its shape looked like the insect.