Know the difference when writing. Many times I’ve seen ordinance used in reference to military ammunition and weapons. It’s isn’t just in fiction either. Here’s a headline from a newspaper:
Unexploded ordinance brought to Fairchild triggers lockdown
Funny thing about this headline, this is what it read as above when it was first posted. Hours later, it was changed to:
Unexploded ordnance brought to Fairchild triggers lockdown
Note the difference?
Ordinance is a law or rule. Something a city council might pass in regard to no livestock within the city limits or no loud stereos after 10pm. That is what an ordinance is.
Have some fun. Look for this misuse in television shows, movies, and books. Have a little private chuckle safe in the knowledge that you know the difference between two words that sound the same but mean totally different things.
Think this doesn’t happen? NCIS, the highly vaunted series about the Naval Criminal Investigative Service, had a scene where the actors walked past a sign that read ‘Explosive Ordinance Disposal‘, yeah, that was a huge laugh. Apparently, those ordinances that are passed become explosive and need to be disposed of properly.