A noncommissioned officer who instructs recruits in military marching and discipline WordNet 3.0 & Open English WordNet

A drill instructor is a non-commissioned officer in the armed forces, fire department, or police forces with specific duties that vary by country. Wikipedia

A non-commissioned officer in many military or police forces Wikipedia Disambiguation

Military training officer Wikidata

The generic term for the principal instructor of fresh military recruits undergoing basic training in the various branches of the United States military, routinely abbreviated to the initialism DI; always filled by enlisted personnel (a sergeant or petty officer). Wiktionary