An ordinance is a rule or law, usually one passed by a local authority such as a city. Ordnance is military weaponry and ammunition. Memory hook: ordinance has an extra syllable for the extra paperwork, while ordnance is the shorter, heavier word for things that explode.
The core difference
An ordinance is a law or official order, whereas ordnance is military weapons, ammunition and related equipment.
- ordinance — a law or authoritative order, especially a local one: The council passed an ordinance banning fires in the park.
- ordnance — military weapons, ammunition and related equipment: Unexploded ordnance from the war still turns up in the fields.
How to tell them apart
The two words are historically related: ordnance is a shortened form of ordinance, which once also covered military equipment before that sense narrowed to weapons and artillery. Today they are treated as separate words, so it matters which you choose.
The mix-up is common in news and legal writing. Think of ordinance as related to order, as in an official order, and remember that ordnance is the one dropped from the sky or stored in a bunker. If a sentence involves a council, a rule or a fine, it is almost certainly ordinance.
