Here's something I learned about 10 minutes ago. According to OED online, conciseness has just one definition: "Concise quality; brevity, terseness." Concision has three definitions:
- The action of cutting to pieces or cutting away; mutilation.
- In Phil. iii. 2 (from the Geneva version of 1557 onward) it translates Gr. ‘cutting off, cutting up’, used there instead of ‘circumcision’, and applied contemptuously to the Judaizing Christians.
If you use concision to mean conciseness, the reader will probably figure out the meaning from the context. But use conciseness, and the reader won't have to figure out your meaning; you'll subtract one chance that the reader will misunderstand your message.
1The funny-looking letters are Greek. I hope they show properly on your computer.