catechism

The oldest source is Greek katēkhein, literally meaning to sound down, resound, or instruct by word of mouth. In the Greek-speaking eastern Mediterranean, the verb was tied to oral teaching and repeated hearing. From it came katēkhismos, instruction given aloud. The sound-image mattered from the beginning.

Early Christians adopted the family for religious teaching. By late antiquity, catechizare in ecclesiastical Latin meant to instruct converts orally in the faith. Catechismus then named the body or method of that instruction. The word moved with the Church rather than with trade.

In the 16th century, the Reformation made catechisms famous across Europe. Martin Luther issued his Large Catechism and Small Catechism in 1529, and other churches answered with their own. English took catechism through Latin and French forms in this era of printed doctrine. What had been spoken teaching became a fixed book and a fixed format.

That history explains the modern double sense. A catechism is still a manual of basic religious doctrine, especially in question-and-answer form. By extension, it can mean any set of formal principles learned by repetition. An echo-word became a drill-word.